reduce-historical/r35/lib/crack2.red

%  Applications of CRACK


%********************************************************************
module decomposition$
%********************************************************************
%  Routines for decomposition of PDE's
%  Author: Thomas Wolf
%  June 1991

fluid '(fname_ nfct_);

algebraic procedure decomp(problem,runmode);
begin scalar i,j,k,de,m,n,x,y,yy,yyy,new!_d!_yk,as,sol,h1,h2,dep$
  lisp put('d!_y,'simpfn, 'simpiden)$
  lisp put('u!#,'simpfn, 'simpiden)$
  de:=first problem$ problem:=rest problem$
  y :=first problem$ problem:=rest problem$
  x :=first problem$ problem:=0$
  as:=first runmode$ runmode:=rest runmode$
  fl:=first runmode$ runmode:=0$
  symbolic write "Differential factorization of:  "$
  lisp terpri()$
  write de$
           % order of the de
  n :=lisp highdiff(reval algebraic de, reval algebraic y,
                    reval algebraic x)$
  k:=1;    % factorization into a first-order ODE + ...
  clear d1!_,d2!_,d3!_;
  de:=rhs de - lhs de;
  for i:=2:n do <<de:=sub(df(y,x,i)=d!_y(i),de);
                  as:=sub(df(y,x,i)=d!_y(i),as)>>;
  de:=sub(df(y,x)=d!_y(1),de);
  as:=sub(df(y,x)=d!_y(1),as);
  yy:=lisp if atom (yyy:=reval algebraic y) then yyy
                                            else car yyy;
  if (y neq yy) then << let y=yy; de:=de; as:=as; clear y; y:=yy >>;
  depend a!#,x;
  depend b!#,x;
  depend c!#,x;
  depend d!#,y;
  d!_y(k):=
  if as=1 then <<fl:={a!#,d!#};     a!#*d!#            >> else
  if as=2 then <<fl:={a!#,b!#};     a!#*y+b!#          >> else
  if as=3 then <<fl:={a!#,b!#};     a!#*y**d1!_+b!#*y  >> else
  if as=4 then <<fl:={a!#,b!#,c!#}; a!#*y**2+b!#*y+c!# >> else
  as$
  vl:={y,x};
  for i:=1:(k-1) do vl:=.(d!_y(i),vl);
  new!_d!_yk:=d!_y(k)$
  write "The ansatz: ", df(y,x)," = ",d!_y(k);
  if df(yy,x) neq 0 then <<dep:=1;nodepend yy,x>> else dep:=0;
  for m:=k+1:n do
  d!_y(m):=df(d!_y(m-1),x)+df(d!_y(m-1),y)*d!_y(1)+
           for j:=1:k-1 sum df(d!_y(m-1),d!_y(j))*d!_y(j+1);
  de:=de;
  for m:=k:n do clear d!_y(m);

  sol:=crack({de},{},fl,vl);   % first, because {a} is linear
  if sol={} then <<
   write"There exists no such factorization.";
   return {} >>
            else <<
   sol:=first sol;
   h1:=second sol;
   for each h2 in h1 do
   if symbolic (not atom algebraic h2) then
   if symbolic (equal(car algebraic h2,'equal)) then
   new!_d!_yk:=sub(h2,new!_d!_yk)$
   if dep=1 then depend yy,x;
   new!_d!_yk:=sub(d!_y(1)=df(y,x),new!_d!_yk);
   for i:=2:n do new!_d!_yk:=sub(d!_y(i)=df(y,x,i),new!_d!_yk);
   h1:=first sol$
   if h1 neq {} then
   <<write "Remaining conditions:";
     while h1 neq {} do <<write"0 = ",first h1;h1:=rest h1>> >>;
   !!arbconst:=0;
   h1:=df(y,x,k)-new!_d!_yk  ;
   h2:=first odesolve(h1,y,x);
   if h1=h2 then write "The solution of ",df(y,x,k)," = ",new!_d!_yk
            else
   <<yyy:=mkid(lisp fname!_,lisp nfct!_);
     h2:=sub(arbconst(1)=yyy,h2);
     lisp(nfct!_:=add1 nfct!_);
     write "The solution ",h2>>;
   if length third sol<(n-k)                         then
   write "is a special solution of the original ODE" else
   if length first sol = 0                             then
   write "is the general solution of the original ODE" else
   write "is a solution of the original ODE";
   h1:=first sol;
   return {h1,new!_d!_yk,third sol} >>
end$

symbolic procedure lesedec;
begin scalar c;
  <<rds nil;wrs nil;
    terpri();write "Input: "$
    c:=xread(nil);
    if ifl!* then rds cadr ifl!*;
    if ofl!* then wrs cdr ofl!* >>;
return c
end$

endmodule$


%********************************************************************
module firstintegral$
%********************************************************************
%  Routines for finding first integrals of PDE's
%  Author: Thomas Wolf
%  June 1991

fluid '(print_);

algebraic procedure firint(problem,runmode);
%de...das DGL-Problem, n...Ordnung der DGL, r...Grad des Ansatzes
begin scalar de,n,x,y,yy,yyy,fl,vl,f!_new,a,sol,h1,h2,co,newfl,fi,dg,
             dep$
  symbolic put('d!_y,'simpfn,'simpiden)$
  de:=first problem$ problem:=rest problem$
  y:=first problem$ problem:=rest problem$
  x:=first problem$ problem:=0$
  fi:=first runmode$ runmode:=rest runmode$
  fl:=first runmode$ runmode:=rest runmode$
  dg:=first runmode$ runmode:=0$
  vl:={}$
  lisp terpri()$
  write "Determination of a first integral for: ";
  write de;
  n :=lisp highdiff(reval algebraic de, reval algebraic y,
                    reval algebraic x)$
  de:=rhs de;
  for i:=2:n do <<de:=sub(df(y,x,i)=d!_y(i),de);
                  fi:=sub(df(y,x,i)=d!_y(i),fi)>>;
  de:=sub(df(y,x)=d!_y(1),de);
  fi:=sub(df(y,x)=d!_y(1),fi);
  yy:=lisp if atom (yyy:=caaar caadr algebraic y) then yyy
                                                  else car yyy;
  if (y neq yy) then << let y=yy; de:=de; fi:=fi; clear y; y:=yy >>;
  if freeof(de,d!_y(n)) then
  <<d!_y(n):=de;
  if fi=0 then begin
    fi:=polyans(n-1,dg,x,y,d!_y,h!_);
    fl:=second fi;
    fi:=first fi
  end;
  symbolic if print_ then
  algebraic write "of the type: ",sub(d!_y(1)=df(y,x),fi) ;
  if df(yy,x) neq 0 then <<dep:=1;nodepend yy,x>> else dep:=0;
  a:=df(fi,x)+df(fi,y)*d!_y(1)+
    for k:=1:n-1 sum (df(fi,d!_y(k))*d!_y(k+1));
  vl:=.(d!_y(n-1),vl);
  clear d!_y(n);
  sol:=crack({a},{},fl,vl);   % first, because {a} is linear
  if sol={} then <<
   write"There exists no such first integral.";
   return {} >>
            else <<
   sol:=first sol;
   h1:=second sol;
   for each h2 in h1 do
   % if symbolic (not atom algebraic h2) then
   % if symbolic (equal(car algebraic h2,'equal)) then
   fi:=sub(h2,fi)$
   h1:=third sol;
   newfl:={};
   for each h2 in h1 do
   if (df(h2,y) eq 0) and (df(h2,x) eq 0) and (df(h2,d!_y 1) eq 0) then
   <<on ratarg;
     co:=coeffn(fi,h2,1);
     if freeof(co,x) and freeof(co,y) and freeof(co,d!_y 1) and
        deg(fi-co*h2,h2)=0 then fi:=sub(h2=0,fi)
                           else newfl:=.(h2,newfl)>>;
   h1:=newfl;
   newfl:={};
   for each h2 in h1 do
   if (df(h2,y) eq 0) and (df(h2,x) eq 0) and (df(h2,d!_y 1) eq 0) then
   if df(fi/h2,h2)=0 then fi:=sub(h2=1,fi)
                     else newfl:=.(h2,newfl);
   if freeof(fi,x) and freeof(fi,y) and freeof(fi,d!_y 1) then fi:=0;
   printco(first(sol));
   if dep=1 then depend yy,x;
   if fi neq 0 then
     <<co:=df(fi,d!_y 1);
     fi:=sub(d!_y(1)=df(y,x),fi);
     co:=sub(d!_y(1)=df(y,x),co);
     for i:=2:n do
       <<fi:=sub(d!_y(i)=df(y,x,i),fi);
       co:=sub(d!_y(i)=df(y,x,i),co)>>;
     write"A first integral is:  ",fi;
     write"and an integrating factor:  ",co;
     if (third sol neq {}) then
       <<lisp terpri();
       if (first sol neq {})
       then lisp write "functions and constants to be determined: "
       else lisp write "free constants: ";
                        lisp fctprint(cdr reval algebraic newfl)>>
      >>
   else write"There exists no such first integral.";
   return {first sol,fi,newfl}>> >>
 else
    <<write "Implicit d.e. ! "$
    return {{},{},{}}>>
end$

algebraic procedure printco(sol);
if (sol neq {}) then
<<write "Remaining conditions:";
  while sol neq {} do <<write"0 = ",first sol;sol:=rest sol>> >>$

endmodule$

%********************************************************************
module lagrangian$
%********************************************************************
%  Routines for finding a Lagrangian for a given PDE
%  Author: Thomas Wolf
%  June 1991

fluid '(nfct_ print_);

symbolic operator deprint$
symbolic operator newfct$
symbolic operator freeoflist$

algebraic procedure Hamilton(L,qlist,x)$

comment:
This is a procedure which for a given first order Lagrangian L in the
unknown functions given in the list q of the variable x
- calculates the velocities in terms of the corresponding generalized
  impulses p_ and the Hamiltonian H(p_,q,x),
- formulates the corresponding Hamilton Jacobi equation for a
  for an action function S_.
After execution the q's in qlist are scalars independent of x! ;

begin
  scalar qcopy,i,j,q,dq,plist,n,dqlist,found,SF,sans,solved,H;
  symbolic put('p_,'simpfn,'simpiden)$      % p_(i) : general. impulses
  symbolic put('dq_,'simpfn,'simpiden)$     % dq(i) : dq/dx

  n:=length qlist; % the number of functions q

  % substitution of df(qi,x) by dq_(i) in the Lagrangian
  qcopy:=qlist;
  for i:=1:n do <<
    q:=first qcopy; qcopy:=rest qcopy;
    L:=sub(df(q,x)=dq_(i),L)>>;

  % expressing dq_(i) by the general. impulses p_(j) and the q's
  plist:={}; dqlist:={};
  for i:=1:n do <<plist:=.(df(L,dq_(i)) - p_(i), plist);
                  dqlist:=.(dq_(i),dqlist)>>;
  dqlist:=solve(plist,dqlist);
  dq:=first dqlist;
  if symbolic(car algebraic(dq))=LIST then dqlist:=dq;
  if lisp(print_) then write"The velocities: ",dqlist;

  % Test for solubility:
  solved:=t;
  if length dqlist = 0 then solved:=nil
                       else <<
    for i:=1:n do <<
      qcopy:=dqlist;
      found:=nil;
      while (not found) and (qcopy neq {}) do <<
        dq:=first qcopy; qcopy:=rest qcopy;
        if (lhs dq) = dq_(i) then found:=t >> >>;
    if found=nil then solved:=nil>>;

  if solved=nil then <<
    if lisp(print_) then
    write
   " The equations p_ = dL/d(dq/dx) could not be solved for the dq/dx.";
    return nil
  >>            else <<

   % the Hamiltonian as a function of p_, q, x
    H := sub(dqlist, -L + for i:=1:n sum p_(i)*dq_(i));
    if lisp(print_) then <<
      write "The Hamiltonian with P_(i) as the canonical impulses: ";
      on factor,mcd;
      write "H = ",H;
      off factor,mcd
    >>;

    % The Hamiltonian-Jacobi equation
    HJ := H;
    SF:=first sepans(0,{},.(x,qlist),s);
    qcopy:=qlist;
    for i:=1:n do <<q:=first qcopy;qcopy:=rest qcopy;
                    HJ:=sub(p_(i) = df(SF,q), HJ)>>;
    HJ := num(df(SF,x) + HJ);
    if lisp(print_) then <<
      write "The general Hamilton-Jacobi equation for the action S_:";
      write " 0 = ",HJ
    >>;

    % The q's of qlist are becomming independent of x
    qcopy:=qlist;
    while qcopy neq {} do <<
      nodepend first qcopy, x;
      qcopy:=rest qcopy >>;

    return {HJ, SF, H, dqlist}
  >>
end$ % of Hamilton

%----------------------------

algebraic procedure drop_const(oldsoln, varlist, additive)$

comment
  oldsoln is the output of a CRACK call. In all solutions functions
  which are independent of all elements of varlist are dropped from
  the list of free functions/constants and
  - set to zero if additive=t and they are additive or
  - set to 1 if additive=nil and they are multiplicative;

begin
  scalar soln, sl, fncn, h1, h2, newfl, vcopy, constnt, v, fcopy,f1,co;
  soln := {};
  off mcd;
  while oldsoln neq {} do <<
    sl := first oldsoln; oldsoln := rest oldsoln;
    fncn := second sl;
    h1 := third sl;
    newfl:={};
    for each h2 in h1 do <<
              % is h2 constant ?
      vcopy := varlist;
      constnt := t;
      while constnt and (vcopy neq {}) do <<
        v := first vcopy; vcopy := rest vcopy;
        if not freeof(co,v) then constnt := nil
      >>;
      if constnt then
      if (not freeof(first sl, h2)) or freeof(fncn, h2)
      then constnt := nil;
      if constnt then <<
          % is the coefficient of h2 constant in all solved expressions
          % and occurs h2 only linear ?
        fcopy := fncn;
        while constnt and (fcopy neq {}) do <<
          f1 := rhs first fcopy; fcopy := rest fcopy;
          co:=coeffn(f1,h2,1);
          if (not freeof(co,h2))                               or
             (     additive  and (not freeof(f1 - co*h2, h2))) or
             ((not additive) and ((f1 - co*h2) neq 0))
          then constnt := nil;
          if constnt and additive then <<
            vcopy := varlist;
            while constnt and (vcopy neq {}) do <<
              v := first vcopy; vcopy := rest vcopy;
              if not freeof(co,v) then constnt := nil
            >>
          >>
        >>
      >>;
      if constnt then if additive then fncn := sub(h2=0, fncn)
                                  else fncn := sub(h2=1, fncn)
                 else newfl := cons(h2, newfl)
    >>;
    soln := cons({first sl, fncn, newfl}, soln)
  >>;
  on mcd;
  return soln
end$ % of drop_add_const

%----------------------------

algebraic procedure solve_HJ(L,qlist,x)$

comment   This Procedure
- makes a separation ansatz for S:
  S(x,qi,Qj) = S1(x,q1,Qj) + S2(x,q2,Qj) +...+ Sn(x,qn,Qj),   or
  S(  qi,Qj) = S1(  q1,Qj) + S2(  q2,Qj) +...+ Sn(  qn,Qj)
  if  dL/dx = 0 or
  S(x,q) = S1(x) + S2(q)   or
  S(x,q) = S1(x)*S2(q) + ...
  if qlist contains only one function q of x.

- calls the package CRACK for solving the resulting conditions
  for the Si,
- finds the general solution for qi(x) from
        dS/dQi = - Pi = constant                                    (*)
  d .. partial derivative,  D .. total derivative
  where the Qi are the (non-trivial and non-additive) constants of
  integration provided by the package CRACK when solving for Si where
  Pi are further constants of integration. The qi have to be solved
  algebraically from (*).

  (*) follows according to the general theory if one regards S(x,qi,Qj)
  as the generating function S(x,qi,Qj) of a canonical transformation
  such that after the transformation the new Hamiltonian is a function
  of Qi only such that DQi/Dt = 0 --> new Qj = constants -->
  new H = constant --> DPj/Dx = 0 -->
  new Pi = constant;

begin
  scalar Ham, sans, a, SF, SFans, xcycl, SAnsatz, undet,
         clist, reslt, el1, el2, K_, fnlsys, xqlist;

  Ham := Hamilton(L,qlist,x);
  if Ham neq nil then <<
    SF := second Ham;
              % special simplified treatment if x is a cyclix variable
    if freeof(third Ham,x) then xcycl:=t
                           else xcycl:=nil;
              % Chosing a suitable ansatz
    if length(qlist)=1 then
    if xcycl then sans:=sepans(8,       qlist ,{},s) % S=K_*x  + S2(q1)
             else sans:=sepans(8,cons(x,qlist),{},s) % S=S1(x) + S2(q1)
                       else
    if xcycl then sans:=sepans(8,qlist, {},s)
                               % S = K_*x + S1(q1) +...+ Sn(qn)
             else sans:=sepans(8,qlist,{x},s);
                               % S = S1(q1,x) + ... + Sn(qn,x)

    if xcycl then begin
     K_:=newfct(c,nil,lisp nfct_);
     lisp(nfct_:=add1 nfct_);
     SAnsatz := K_*x + first sans;
    end      else begin
     SAnsatz := first sans;
    end;

              % The Hamilton-Jacobi equation
    a:= sub(SF=SAnsatz, first Ham);
    if lisp(print_) then <<
      write "The ansatz for the action: S_ = ",SAnsatz;
      if xcycl then
      write "           with ",K_,
            " = constant ( = H because ",x," is cyclic)";
      write "gives for the Hamilton-Jacobi equation:";
      write " 0 = ",a;
      write "which is to be solved.";
    >>;
              % Solving it and dropping additive constants
    sans := second sans;
    xqlist := .(x,qlist);
    if xcycl then sans:=.(K_, sans);
    reslt := drop_const(crack({a}, {}, sans, {}), xqlist, t);
    if reslt neq {} then <<
      % first because only one solution is expected for the linear HJ
      reslt := first reslt;
      undet := third reslt;
      if lisp(print_) then write "result = ",reslt;
      SAnsatz := sub(second reslt, SAnsatz);
      if lisp(print_) then write "The action  S_ = ", SAnsatz;

              % Formulating the final solution by differentiating S
      fnlsys:={};
      clist:={};    % undet muss K_ enthalten
                    % if xcycl then undet:=.(K_, undet);
      for each el1 in undet do
      if freeoflist(el1,xqlist) then clist:=.(el1,clist);

      for each el1 in undet do
      if (not freeof(sans,el1)) and
         freeof(clist,el1)      and
       (not freeof(first reslt,el1)) then
      for each el2 in clist do depend el1,el2;

      for each el1 in clist do <<
        fnlsys:=.(newfct(c,nil,lisp nfct_)-df(SAnsatz,el1),fnlsys);
        lisp(nfct_:=add1 nfct_);
      >>;

      if lisp(print_) then <<
        write"The solution in implicit form is:";
        for each el1 in fnlsys do write"0 = ",el1$
      >>;
%      fnlsys:=solve(fnlsys,qlist);
%      if lisp(print_) and (fnlsys neq {}) then <<
%        write
%        "The solution in explicit form is (if SOLVE could solve it):";
%        for each el1 in fnlsys do write el1$
%      >>

    >>

  >>
end$  % of solve_HJ

%----------------------------

algebraic procedure lagran(problem,runmode)$
% sol = false : determination of the Lagrangian only
% sol = true  : also transformation to L = y^'2
% returns return of lagfcn
begin scalar de,n,fl,vl,lg,x,y,yy,yyy,loes,k,a,b,ll,h1,h2,dep$
  scalar imp,y!',ham,sf$      % for the Hamiltonian part
  symbolic put('d!_y,'simpfn,'simpiden)$
  de:=first problem$ problem:=rest problem$
  y :=first problem$ problem:=rest problem$
  x :=first problem$ problem:=0$
  lg:=first runmode$ runmode:=rest runmode$
  fl:=first runmode$ runmode:=0$
  vl:={};
  symbolic write "Determination of a Lagrangian L for:";
  lisp terpri()$
  write de$
  n :=lisp car reverse caaar caadr algebraic lhs de$
  if n eq x then n:=1;
  de:=rhs de;
  for i:=2:n do <<de:=sub(df(y,x,i)=d!_y(i),de);
                  lg:=sub(df(y,x,i)=d!_y(i),lg)>>;
  de:=sub(df(y,x)=d!_y(1),de);
  lg:=sub(df(y,x)=d!_y(1),lg);
  yy:=lisp if atom (yyy:=caaar caadr algebraic y) then yyy
                                                  else car yyy;
  if (y neq yy) then << let y=yy; de:=de; lg:=lg; clear y; y:=yy >>;
  if lg=0 then
  <<depend u!_,x,y;
    depend v!_,x,y;
    lg:=u!_*d!_y 1**2+v!_;
    fl:=append({u!_,v!_},fl)>>$
  if n>1 then vl:=.(d!_y(n-1),vl)$
  symbolic(if print!_ neq nil then
  algebraic write "The ansatz:  L = ",sub(d!_y(1)=df(y,x),lg) )$
  if df(yy,x) neq 0 then <<dep:=1;nodepend yy,x>> else dep:=0;
  loes:=lagfcn(de,n,x,y,fl,vl,lg);
  lg:=second loes;
  if dep=1 then depend yy,x;
  if (lg eq 0) then write"No Lagrangian of this structure!" else
  <<on factor,mcd;
    lg := sub(d!_y(1)=df(y,x),lg)$
    write "The solution:  L = ",lg$
    off factor; % ,mcd;
    if (first loes neq {})                     then
    <<write "Remaining conditions: "$
      for each s in first loes do symbolic deprint list algebraic s>>
                                               else
if nil then
    solve_HJ(lg,{y},x);
  >>;
  return loes
end$   % of lagran

%----------------------------

algebraic procedure lagfcn(p,n,x,y,fl,vl,lg);
%determines the Lagrangian
%returns {{necessary eq.s},{suff. equ.s},Lagrangian,{free functions}}
begin scalar h1,h2,newfl,co$
  h1:=df(lg,d!_y 1,x)+df(lg,d!_y 1,y)*d!_y 1-df(lg,y)+df(lg,d!_y 1,2)*p;
  p:= crack({h1},{},fl,vl)$   % first, because {h1} is linear

  p:=drop_const(p, {d!_y,y}, t);       % dropping the divergenz term
  p:=drop_const(p, {d!_y,y,x}, nil);   % dropping the multipli. constant

  if p={} then p:={{},{v_=0,u_=0},{}}
          else p:=first p;

  h1:=second p;
  for each h2 in h1 do
  if symbolic (not atom algebraic h2) then
  if symbolic (equal(car algebraic h2,'equal)) then
  lg:=sub(h2,lg)$

  return {first p,lg,third p}
end$


endmodule$


load_package odesolve$
load_package ezgcd$
load_package factor$

%********************************************************************
module pdesymmetry$
%********************************************************************
%  Routines for finding Symmetries for PDE's
%  Author: Thomas Wolf
%  August 1993

fluid '(logoprint_ print_);

% The algebraic operator NPRIMITIVE returns the
% numerically-primitive part of any expression.
% It is defined as a simpfn in EZGCD.

symbolic operator ncontent$
symbolic procedure ncontent p$
% Return numeric content of expression p
% based on simpnprimitive in ezgcd.
<< p := simp!* p;
   if polyzerop(numr p) then 0 else
   mk!*sq(numeric!-content numr p ./ numeric!-content denr p)
>>$

symbolic operator totdeg$
symbolic procedure totdeg(p,f)$
%   Ordnung (total) der hoechsten Ableitung von f im Ausdruck p
eval(cons('PLUS,ldiff1(car ldifftot(reval p,reval f),fctargs reval f)))$

symbolic procedure diffreltot(p,q,v)$
%   liefert komplizierteren Differentialausdruck$
if diffreltotp(p,q,v) then q
                   else p$

symbolic procedure diffreltotp(p,q,v)$
%   liefert t, falls p einfacherer Differentialausdruck, sonst nil
%   p, q Paare (liste.power), v Liste der Variablen
%   liste Liste aus Var. und Ordn. der Ableit. in Diff.ausdr.,
%   power Potenz des Differentialausdrucks
begin scalar n,m$
m:=eval(cons('PLUS,ldiff1(car p,v)))$
n:=eval(cons('PLUS,ldiff1(car q,v)))$
return
 if m<n then t
 else if n<m then nil
      else diffrelp(p,q,v)$
end$

symbolic procedure ldifftot(p,f)$
%  leading derivative total degree ordering
%  liefert Liste der Variablen + Ordnungen mit Potenz
%  p Ausdruck in LISP - Notation, f Funktion
ldifftot1(p,f,fctargs f)$

symbolic procedure ldifftot1(p,f,vl)$
%  liefert Liste der Variablen + Ordnungen mit Potenz
%  p Ausdruck in LISP - Notation, f Funktion, lv Variablenliste
begin scalar a$
a:=cons(nil,0)$
if not atom p then
if member(car p,list('EXPT,'PLUS,'MINUS,'TIMES,
          'QUOTIENT,'DF,'EQUAL)) then
                                        %  erlaubte Funktionen
        <<if (car p='PLUS) or (car p='TIMES) or (car p='QUOTIENT)
             or (car p='EQUAL) then
                <<p:=cdr p$
                while p do
                        <<a:=diffreltot(ldifftot1(car p,f,vl),a,vl)$
                        p:=cdr p>> >>
        else if car p='MINUS then
                a:=ldifftot1(cadr p,f,vl)
        else if car p='EXPT then        %  Exponent
                        if numberp caddr p then
                        <<a:=ldifftot1(cadr p,f,vl)$
                        a:=cons(car a,times(caddr p,cdr a))>>
                        else a:=cons(nil,0)
                                        %  Poetenz aus Basis wird mit
                                        %  Potenz multipliziert
        else if car p='DF then          %  Ableitung
                if cadr p=f then a:=cons(cddr p,1)
                                        %  f wird differenziert?
                else a:=cons(nil,0)>>   %  sonst Konstante bzgl. f
else if p=f then a:=cons(nil,1)
                                        %  Funktion selbst
        else a:=cons(nil,0)             %  alle uebrigen Fkt. werden
else if p=f then a:=cons(nil,1)$        %  wie Konstante behandelt
return a
end$

% ---------------------------------------------------------------------

% Bei jedem totdiff-Aufruf pruefen, ob evtl. kuerzere dylist reicht
% evtl die combidiff-Kette und combi nicht mit in dylist, sond. erst in
% prolong jedesmal frisch generieren.

symbolic operator desort;

algebraic procedure nextdy(revx,xlist,dy)$
% generates all first order derivatives of lhs dy
% revx = reverse xlist; xlist is the list of variables;
%                       dy the old derivative
begin
  scalar x,n,ldy,rdy,ldyx,sublist;
  x:=first revx; revx:=rest revx;
  sublist:={};
  ldy:=lhs dy;
  rdy:=rhs dy;

  while lisp(not member(prepsq simp!* algebraic x,
             prepsq simp!* algebraic ldy))
        and (revx neq {}) do
  <<x:=first revx; revx:=rest revx>>;

  n:=length xlist;
  if revx neq {} then                % dy is not the function itself
  while first xlist neq x do xlist:=rest xlist;
  xlist:=reverse xlist;

  % New higher derivatives
  while xlist neq {} do
  <<x:=first xlist;
    ldyx:=df(ldy,x);
    sublist:=cons(ldyx=mkid(mkid(rdy,!|),n), sublist);
    n:=n-1;
    xlist:=rest xlist
  >>;
  return sublist
end$


algebraic procedure subdif1(xlist,ylist,ordr)$
% A list of lists of derivatives of one order for all functions
begin
 scalar allsub,revx,i,el,oldsub,newsub;
 revx:=reverse xlist;
 allsub:={};
 oldsub:= for each y in ylist collect y=y;
 for i:=1:ordr do      %  i is the order of next substitutions
 <<oldsub:=for each el in oldsub join nextdy(revx,xlist,el);
   allsub:=cons(oldsub,allsub)
 >>;
 return allsub
end$


algebraic procedure subdif2(xlist,ylist,ordr)$
% A list of for each function one list of lists of derivatives of one
% order
begin
  scalar allsub,revx,i,el,oldsub,newsub;
  revx:=reverse xlist;
  return
  for each y in ylist collect
  <<allsub:={};
    oldsub:={y=y};
    for i:=1:ordr do   %  i is the order of next substitutions
    <<oldsub:=for each el in oldsub join nextdy(revx,xlist,el);
      allsub:=cons(oldsub,allsub)
    >>;
    allsub
  >>
end$

symbolic operator combidif$

symbolic procedure combidif(s)$
% we want to extract the list of derivatives from
begin scalar temp,ans,no,n1,done;
  s:=reval s; % to guarantee s is in true prefix form
  temp:=reverse explode s;

  while not null temp do
  <<n1:=<<no:=nil;
          while (not null temp) and (not eqcar(temp,'!|)) do
          <<no:=car temp . no;temp:=cdr temp>>;
          compress no
        >>;
    if (not fixp n1) then n1:=intern n1;
    ans:=n1 . ans;
    if eqcar(temp,'!|) then <<temp:=cdr temp; temp:=cdr temp>>;
  >>;
  return ans
end$


symbolic operator combi;

symbolic  procedure combi(ilist)$
% ilist is a list of indexes (of variables of a partial derivative)
% and returns length!/k1!/k2!../ki! where kj! is the multiplicity of j.
begin
  integer n0,n1,n2,n3;
  n1:=1;
  ilist:=cdr ilist;
  while ilist do
  <<n0:=n0+1;n1:=n1*n0;
    if car ilist = n2 then <<n3:=n3+1; n1:=n1/n3>>
                      else <<n2:=car ilist; n3:=1>>;
    ilist:=cdr ilist>>;
  return n1
end$

symbolic operator dif$

symbolic procedure dif(s,n)$
% e.g.:   dif(fnc!|1!|3!|3!|4, 3) --> fnc!|1!|3!|3!|3!|4
begin scalar temp,ans,no,n1,n2,done;
  s:=reval s; % to guarantee s is in true prefix form
  temp:=reverse explode s;
  n2:=reval n;
  n2:=explode n2;

  while (not null temp) and (not done) do
  <<n1:=<<no:=nil;
          while (not null temp) and (not eqcar(temp,'!|)) do
          <<no:=car temp . no;temp:=cdr temp>>;
          compress no
        >>;
    if (not fixp n1) or ((fixp n1) and (n1 leq n)) then
    <<ans:=nconc(n2,ans); ans:='!| . ans; ans:='!! . ans; done:=t>>;
    ans:=nconc(no,ans);
    if eqcar(temp,'!|) then <<ans:='!| . ans; ans:='!! . ans;
                              temp:=cdr temp; temp:=cdr temp>>;
  >>;
  return intern compress nconc(reverse temp,ans);
end$

symbolic operator totdif;

symbolic procedure totdif(s,x,n,dylist)$
% total derivative of s(x,dylist) w.r.t. x which is the n'th variable
begin
  scalar tdf,el1,el2;
  tdf:=simpdf {s,x};
  <<dylist:=cdr dylist;
    while dylist do
    <<el1:=cdar dylist;dylist:=cdr dylist;
      while el1 do
      <<el2:=car el1;el1:=cdr el1;
        tdf:=addsq(tdf ,multsq( simp!* dif(el2,n), simpdf {s,el2}))
      >>
    >>
  >>;
  return prepsq tdf
end$

symbolic operator totdiff$

symbolic procedure totdiff(s,n,dysublist)$
% total derivative of s(x,dylist) w.r.t. the n'th x-variable and
% using only highest derivatives
begin
  scalar tdf,el2;
  tdf:=simp!* 0;
  dysublist:=cdr dysublist;
  while dysublist do
  <<el2:=car dysublist;dysublist:=cdr dysublist;
    tdf:=addsq(tdf ,multsq( simp!* dif(el2,n), simpdf {s,el2}))
  >>;
  return prepsq tdf
end$


algebraic procedure depnd(y,xlist)$
for each xx in xlist do
for each x  in xx    do depend y,x$


algebraic procedure transeq(eqn,xlist,ylist,sb)$
<<for each el1 in sb do eqn:=sub(el1,eqn);
  for each el1 in ylist do
  for each el2 in xlist do nodepend el1,el2;
  eqn>>$


algebraic procedure dirdiv(problem,runmode)$

 comment
 problem ~ {eqn               % equation
            { y1, y2, ...},   % functions
            { x1, x2, ...} }  % variables
 runmode ~ {ansatz, flist}

 ansatz=nil then
   standard ansatz:
       H_(all variables + all functions + all derivatives < ordr.)
       v_x1, v_x2, ..., v_(n+1) (all variables)
 else
   ansatz={H_=...,v_x1=...,v_x2=...}
   flist ={unknown functions in ansatz}
 ansatz: equ = v_(n+1) + for all i sum v_xi*df(h_,xi);

begin
  scalar sb,el1,el2,dy1list,dy2list,flist,eqlist,h,
         xlist, ylist, ordr, ansatz, cpu, gc;

  cpu:=lisp time()$ gc:=lisp gctime()$

  eqn   := first problem$
  ylist :=second problem$
  xlist := third problem$

  ansatz:= first runmode$
  flist :=second runmode$

  problem:=runmode:=0;

  lisp(<<
  write "----------------------------------------------------",
  "----------------------"$ terpri()$terpri()$
  write"This is DIRDIV - a program for writing a PDE as a directional ";
  write"derivative with a vector depending only on the independent ",
       "variables"$
  terpri()>>);
  write "The PDE under investigation is :";
  write"0 = ",eqn;
  write "for the function(s) : ";
  lisp(<<terpri()$fctprint cdr reval algebraic ylist;
         terpri()$terpri()>>);

  ordr:=0;
  for each e1 in ylist do
  <<n:=totdeg(eqn,e1);
    if n>ordr then ordr:=n>>;
      % Generating a substitution list and doing the substitutions
      % and Functions of ylist become variables
  sb:=subdif1(xlist,ylist,ordr)$
  eqn:=transeq(eqn,xlist,ylist,sb);

            % Lists of partial derivatives
  dy1list:=for each el2 in first sb collect rhs el2;
  dy2list:=ylist . for each el1 in rest sb collect
                   for each el2 in el1 collect rhs el2;

            % Generating the equations
  depnd(h!_,xlist . dy2list);
  if ansatz eq nil then flist:={h!_};
  n:=1;
  for each el1 in xlist do
  <<h:=mkid(v!_,el1);
    depnd(h,{xlist});
    if ansatz eq nil then flist:=h . flist;
    eqn:=eqn-h*totdif(h!_,el1,n,dy2list);
    n:=n+1
  >>;
  h:=mkid(v!_,n);
  depnd(h,{xlist});
  if ansatz eq nil then flist:=h . flist;
  eqn:=eqn-h;

  eqlist:=for each el1 in dy1list collect
  <<h:=coeffn(eqn,el1,1);
    eqn:=eqn-h*el1;h>>;
  eqlist:=eqn . eqlist;

            % Test whether eqn is quasi-linear
  if
  (for each el1 in dy1list product
     if not freeof(eqlist,el1) then 0 else 1)=0
  then return <<write"The equation is not quasilinear! ";
                for each el1 in ylist do depnd(el1,{xlist});
                {}>>;

  if ansatz neq nil then eqlist:=sub(ansatz,eqlist);

  sb:=l1:=el2:=dy1list:=dy2list:=h:=0;
  eqlist:=crack(eqlist,{},flist,{});
  for each el1 in ylist do depnd(el1,{xlist});

  return eqlist

end$

symbolic operator drop$

symbolic procedure drop(a,vl)$
% liefert summe aller terme aus a, die von elementen von vl abhaengen
begin scalar b$
  if not((pairp a) and (car a='PLUS)) then b:=a
                                      else
  <<vl:=cdr vl;             % because vl is an algebraic list
    for each c in cdr a do
    if not freeoflist(c,vl) then b:=cons(c,b)$
    if b then b:=cons('PLUS,reverse b)>>$
  return b$
end$


symbolic operator etamn;

symbolic procedure etamn(u,indxlist,xilist,etalist,revdylist,
                         contact,full)$
% determines etamn recursively
% If length(indxlist)=k then it is assumed that etamn contains at most
% k'th order derivatives, i.e. in revdylist only derivatives up to k'th
% order need to be included. Exception: contact symmetries and k=0 then
% still first oder derivatives are included.
begin
  scalar etam,x,h1,h2,ulist,el,r,cplist,pneta;
  return
    if (length indxlist)<2 then
    <<cplist:=etalist;
      while u neq caddar cplist do cplist:=cdr cplist;
      pneta:=car cplist;                      % = (LIST,eta_yi,yi)
      if null indxlist then cdr pneta
                       else
      <<ulist:=nil;
        cplist:=xilist;
        for h1:=1:(car indxlist)-1 do cplist:=cdr cplist;
        x:=cddar cplist;    % e.g.  x := (v3,3)
        r:=simp!*
           if contact
           then totdif(cadr pneta,car x,cadr x, 'LIST . revdylist)
           else
           if full
           then totdif(cadr pneta,car x,cadr x, 'LIST . cdr revdylist)
           else totdiff(cadr pneta,cadr x,cadr revdylist);
        cplist:=xilist;
        while cplist do
        <<el:=cdar cplist;  % e.g.  el=(xi_z,z,3)
          cplist:=cdr cplist;
          h1:=dif(u,caddr el);
          ulist:=h1 . ulist;
          r:=subtrsq(r, multsq(simp!* h1,simp!*
             if contact
             then totdif(car el,car x,cadr x, 'LIST . revdylist)
             else if full then
                    totdif(car el,car x,cadr x, 'LIST . cdr revdylist)
                  else totdiff(car el,cadr x,cadr revdylist)  ))
        >>;
        % (if not full then drop(r,'LIST . car revdylist) else r) .
        % (reverse ulist)
        prepsq r . (reverse ulist)
      >>
    >>                   else
    <<etam:=etamn(u, cdr indxlist, xilist, etalist,cdr revdylist,
                  contact,full);
      ulist:=nil;
      cplist:=xilist;
      for h1:=1:(car indxlist)-1 do cplist:=cdr cplist;
      x:=cddar cplist;    % e.g.  x := (v3,3)
      r:=simp!*
         if full then totdif(car etam,car x,cadr x,
                             'LIST . cdr revdylist)
                 else totdiff(car etam,cadr x,cadr revdylist);
      etam:=cdr etam;
      cplist:=xilist;
      while cplist do
      <<el:=cadar cplist;     % e.g.  el=xi_z
        cplist:=cdr cplist;
        h1:=dif(car etam,car indxlist);  % e.g.  h1:=u!|i!|m!
        etam:=cdr etam;
        ulist:=h1 . ulist;
        r:=subtrsq(r, multsq(simp!* h1,simp!*
           if full then totdif(el,car x,cadr x,'LIST . cdr revdylist)
                   else totdiff(el,cadr x,cadr revdylist)  ))
      >>;
      % (if not full then drop(r,'LIST . car revdylist) else r) .
      % (reverse ulist)
      prepsq r . (reverse ulist)
    >>
end$ % of etamn


symbolic operator prolong;

symbolic procedure prolong(uik,xilist,etalist,revdylist,minord,
                           contact)$
begin
  scalar indxlist, u, full, l1, l2, i;
  indxlist:=combidif(uik);
  u:=car indxlist; indxlist:=cdr indxlist;
  revdylist:=cdr revdylist;
  l1:=length(indxlist);
  l2:=length(revdylist)-1;
  for i:=1:(l2-l1) do revdylist:=cdr revdylist;
  % revdylist does not need higher derivatives than of order l1
  if minord=0 then full:=t
              else full:=nil;
  return (car etamn(u,indxlist,cdr xilist,cdr etalist,revdylist,contact,
                    full))
end$ % of prolong


algebraic procedure liepde(problem,runmode)$

 comment
 problem ~ {{eq1,eq2, ...},   % equations
            { y1, y2, ...},   % functions
            { x1, x2, ...} }  % variables
 runmode ~ {symord, ansatz, flist}

 if symord=nil then default order of symmetry, i.e.
                    if (one function              ) and
                       (only one equation         ) and
                       (order of equation > 1     ) and
                       ((>1 variable) or (order>2))
                    then symord:=1 (contact s.)
                    else symord:=0 (point s.)
               else symord determines the differential order of xi,
                    eta but must not exceed 0 if more than one
                    dependent variable v

 if ansatz=nil then default ansatz, i.e. xi, eta are functions
                    of xi, yj and derivatives of yj of order upto symord
               else if point symm. then ansatz has to have the form
                                     {xi!_x1=...,...,eta!_y3=...} else
                    if contact- or higher order symm. then ansatz has
                    form
                                     {spot!_=...}
                    flist ={unknown functions in ansatz} ;


begin
  scalar eqlist, ylist, xlist, xilist, etalist, eqn, sb,
         dylist, e1, e2, n, n1,
         n2, n3, symcon, h, flist, deplist, symord, freelist,
         minord, dylen,
         eqlen, subdy, ordr, allsub, truesub, eqcopy1, eqcopy2,
         dycopy, vl,
         occurlist, revdylist, ansatz, cpu, gc, contact;

  cpu:=lisp time()$ gc:=lisp gctime()$

  %--------- extracting input data
  eqlist:= first problem;
  if lisp(atom algebraic eqlist) then eqlist:={eqlist} else
  if lisp(car algebraic eqlist neq 'LIST) then eqlist:={eqlist};

  ylist :=second problem;
  if lisp(atom algebraic ylist) then ylist:={ylist} else
  if lisp(car algebraic ylist neq 'LIST) then ylist:={ylist};

  xlist := third problem;
  if lisp(atom algebraic xlist) then xlist:={xlist} else
  if lisp(car algebraic xlist neq 'LIST) then xlist:={xlist};

  symord:= first runmode$
  ansatz:=second runmode$
  flist := third runmode$

  problem:=runmode:=0;

  eqlist:=for each e1 in eqlist collect
  if lisp(atom e1) then e1 else
  if lisp(car e1 = 'EQUAL) then lhs e1 - rhs e1
                           else e1;

  if length eqlist > 1 then eqlist:=desort eqlist;

  %--------- initial printout
  lisp(if print_ and logoprint_ then <<
    write "-----------------------------------------------",
    "---------------------------"$ terpri()$terpri()$
    write
  "This is LIEPDE - a program for calculating infinitesimal symmetries";
    write "of single ODEs/PDEs and ODE/PDE - systems"; terpri()
  >>                            else terpri());
  write "The ODE/PDE (-system) under investigation is :";
  for each e1 in eqlist do write"0 = ",e1;
  write "for the function(s) : ";
  lisp(<<terpri()$fctprint cdr reval algebraic ylist;
       terpri()$terpri()>>);

  %--------- initializations
  ordr:=0;
  for each e1 in eqlist do
  for each e2 in ylist do
  <<n:=totdeg(e1,e2);
    if n>ordr then ordr:=n>>;
  if symord and (length ylist > 1) and (symord > 0) then
  <<symord:=0;
    write"Only point symmetries are determined if more than one",
         "dependent variable!";
    if ansatz then <<write"Restart with symord=0";halt>>
  >>;
  if symord eq nil then
  if (length ylist = 1              ) and
     ((length xlist > 1) or (ordr>2)) and
     (ordr>1                        ) and
     (length(eqlist)=1              ) then symord:=1
                                      else symord:=0;
  if symord>0 then contact:=t
              else contact:=nil;
  sb:=subdif1(xlist,ylist,ordr)$
  eqlist:=%for each eqn in eqlist collect
          transeq(eqlist,xlist,ylist,sb);

  dylist:=ylist . reverse for each e1 in sb collect
                          for each e2 in e1 collect e3:=rhs e2;
  revdylist:=reverse dylist;  % dylist with decreasing order

  vl:=append(xlist,for each e1 in dylist join e1);

  deplist:=for n:=0:symord collect part(dylist,n+1);
    % list of xi-, eta-variab.

  if not ansatz then flist:={};
  if not contact then <<
    n:=0;
    xilist :=for each e1 in xlist collect
    <<n:=n+1;
      h:=mkid(xi!_ ,e1);
      depnd(h,xlist . deplist);
      if not ansatz then flist:=h . flist;
      {h,e1,n}>>;
    n:=0;
    etalist:=for each e1 in ylist collect
    <<n:=n+1;
      h:=mkid(eta!_,e1);
      depnd(h,xlist . deplist);
      if not ansatz then flist:=h . flist;
      {h,e1}>>
  >>             else <<
    n1:=spot!_;
    depnd(n1,xlist . deplist);
    if ansatz eq nil then flist:=n1 . flist;
    e2:=-n1;
    n:=0;
    xilist:= for each e1 in xlist collect
    <<n:=n+1;
      h:=dif(first ylist,n);
      e2:=e2+df(n1,h)*h;
      {df(n1,h),e1,n}
    >>;
    etalist:={{e2,first ylist}}
    %;write"xilist=",xilist," etalist=",etalist
  >>;

  if ansatz neq nil then <<xilist:=sub(ansatz,xilist);
                           etalist:=sub(ansatz,etalist)>>;

  % Determining a substitution list for highest derivatives from eqlist
  % Substitutions may not be optimal if starting system is not in
  % standard form

  comment: Counting in how many equations each highest
  derivative occurs. Those which do not occur allow Stephani-Trick,
  those which do occur once and there linearly are substituted by that
  equation.

  Because one derivative shall be assigned it must be one of
  the highest derivatives. It could be a lower order derivative
  if substitution is done only finally before solving the
  determining system which would be enough for point symmetries.

  Each equation must be used only once
  Each derivative must be substituted by only one equation
  At first determining the number of occurences of each highest
  derivative.

  If SUB is used for substitution then derivatives could come in
  which are already substituted before. If LET is used, infinite loops
  can occur. ;
  eqcopy1:=eqlist;
  eqlen:=length eqlist;
  dycopy:=part(dylist,length dylist);   % the highest derivatives
  dylen:=length dycopy;
  occurlist:={};
  freelist:={};
  allsub:={};
  truesub:={};
  for n1:=1:dylen do
  <<e1:=part(dycopy,n1);
    n2:=0;     % number of equations in which the derivative e1 occurs
    subdy:={};
    for n3:=1:eqlen do
    if not freeof(part(eqlist,n3),e1) then
    <<n2:=n2+1;
      eqn:=part(eqcopy1,n3);
      if eqn neq 0 then
      <<e2:=coeff(eqn,e1);
        if hipow!*=1 then
        subdy:={n1,n3,e1 = - first e2/second e2} . subdy
      >>
    >>;
    if n2=0 then freelist:=e1 . freelist else
    <<occurlist:=e1 . occurlist;
      if subdy neq {} then if n2=1 then
       <<h:=first subdy;
         truesub:=(third h) . truesub;
         dycopy:=part(dycopy,n1):=0;
         eqcopy1:=part(eqcopy1,second(h)):=0>>
                                   else allsub:=append(subdy,allsub)
    >>
  >>;

  % Taking the remaining known substitutions
  eqn:=h:=subdy:=0;
  for each subdy in allsub do
  if (part( dycopy, first subdy) neq 0) and
     (part(eqcopy1,second subdy) neq 0) then
  <<truesub:=(third subdy) . truesub;
    dycopy :=part( dycopy, first subdy):=0;
    eqcopy1:=part(eqcopy1,second subdy):=0>>;
  allsub:=0;
  % To get the remaining unused equations for substitution as eqcopy2
  % one could
  %    eqcopy2:={};
  %    for each e1 in eqcopy1 do if e1 neq 0 then eqcopy2:=e1 . eqcopy2;
  eqcopy1:=0;dycopy:=0;

  % Determining first short determining equations and solving them
  symcon:={};
  if freelist neq {} then
  for each eqn in eqlist do
  <<eqn:=drop(eqn,first revdylist);
               %dropping all terms without a highest deriv.
    minord:=(length dylist) - 1;
    % Derivatives of freelist cannot be substituted --> no substitution
    h:=for each e2 in occurlist sum
    if freeof(eqn,e2) then 0
                      else prolong(e2,xilist,etalist,revdylist,minord,
                                  contact)
                           * df(eqn,e2);
    for each e2 in freelist do <<e1:=coeffn(h,e2,1);
                                 if e1 neq 0 then symcon:=e1 . symcon>>;
    if lisp(!*time) then
    write "time to formulate conditions: ", lisp time() - cpu,
          " ms    GC time : ", lisp gctime() - gc," ms"$
    h:=first crack(symcon,{},flist,vl);
    cpu:=lisp time()$
    gc:=lisp gctime()$
    % FIRST because the homog. system has at least one and at most
    % one solution
    % Assigning or updating the xi's and eta's:
    symcon:=first h;
    xilist :=sub(second h,xilist);
    etalist:=sub(second h,etalist);
    flist:=third h;
    if lisp(print_ eq nil) then
    <<write"";
      write"Remaining free functions after the last CRACK-run:";
      lisp(fctprint cdr reval algebraic flist);write"">>;
  >>;

  %------------ Determining the full symmetry conditions
  minord:=0;
  h:=1;
  for each eqn in eqlist do
  if h neq {} then
  <<symcon:=((for each e1 in xilist sum first e1 * df(eqn,second e1)) +
              for each e1 in dylist sum
              for each e2 in e1     sum if freeof(eqn, e2) then 0
                                                           else
              prolong(e2,xilist,etalist,revdylist,minord,contact) *
              df(eqn,e2)
            ) . symcon;
    n:=0;
    symcon:=sub(truesub,symcon);
    if lisp(!*time) then
    write "time to formulate conditions: ", lisp time() - cpu,
          " ms    GC time : ", lisp gctime() - gc," ms"$
    h:=crack(symcon,{},flist,vl);
    cpu:=lisp time()$ gc:=lisp gctime()$
    if h neq {} then
    <<h:=first h;
      symcon:=first h;
      xilist :=sub(second h,xilist);
      etalist:=sub(second h,etalist);
      flist:=third h;
      if nil and lisp(print_ eq nil) then
      <<write"";
        write"Remaining free functions after the last CRACK-run:";
        lisp(fctprint cdr reval algebraic flist);write"">>;
    >>
  >>;
  eqn:=sb:=dylist:=e1:=e2:=n:=h:=deplist:=occurlist:=symord:=0;

  %------- Calculation finished
  if h neq {} then
  <<% Dropping free funct.s/const. which do not occur in the xi's
    % or eta's or
    % remaining equations, absorbing numerical constants into free
    % constants
    h:={};
    for each e1 in flist do
    if not freeof({xilist,etalist,symcon},e1) then h:=e1 . h;
    flist:=h;

    for each e1 in flist do <<
      n1:=nil;
      for each e2 in append(xilist,etalist) do <<
        n:=coeffn(first e2,e1,1);
        if n neq 0 then
        if n1=nil then <<n1:=num n; n2:=den n>>
                  else <<
          n:=ncontent(n);
          n1:=gcd(n1,num(n));
          n2:=gcd(n2,den(n))
        >>
      >>;
      if n1 then
      <<xilist :=sub(e1=e1*n2/n1,xilist);
        etalist:=sub(e1=e1*n2/n1,etalist);
        symcon :=sub(e1=e1*n2/n1,symcon)
      >>
    >>;

    %-------- output
    write"The symmetries are: ";
    xilist:=for each el in  xilist collect
    <<e1:=mkid( xi!_,second el); e1:= e1 = first el;write e1;e1>>;

    etalist:=for each el in etalist collect
    <<e1:=mkid(eta!_,second el); e1:= e1 = first el;write e1;e1>>;

    lisp(terpri())$
    if flist neq {} then <<
      write"with constants/functions: ";
      lisp(fctprint cdr reval algebraic flist);write"">>;
    if symcon={} then if flist neq {} then write"which are free." else
                 else
    if lisp(print_) then
    <<write"which still have to satisfy: ";
      lisp(deprint cdr algebraic symcon);
    >>              else
    <<write"which have to satisfy conditions. To see them set ";
      write
      "lisp(print_:= max. number of terms of an equation to print);"
    >>

  >>;
  for each e1 in ylist do depnd(e1,{xlist});
  return {symcon,xilist,etalist,flist}
end$ % of liepde
endmodule$


end$   % of file