1.1.1 `dsolv_dual'
------------------

dsolv_dual(F,V)
     ::  Grobner dual of F.

RETURN
     List

F, V
     List

   * It returns the Grobner dual of F in the ring of polynomials with
     variables V.

   * The ideal generated by F must be primary to the maximal ideal
     generated by V.  If it is not primary to the maximal ideal, then
     this function falls into an infinite loop.

Algorithm: This is an implementation of Algorithm 2.3.14 of the book
[SST].  If we replace variables x, y, ... in the output by log(x),
log(y), ..., then these polynomials in log are solutions of the system
of differential equations F`_(x->x*dx, y->y*dy, ...)'.



     [435] dsolv_dual([y-x^2,y+x^2],[x,y]);
     [x,1]
     [436] dsolv_act(y*dy-sm1_mul(x*dx,x*dx,[x,y]),log(x),[x,y]);
     0
     [437] dsolv_act(y*dy+sm1_mul(x*dx,x*dx,[x,y]),log(x),[x,y]);
     0

     [439] primadec([y^2-x^3,x^2*y^2],[x,y]);
     [[[y^2-x^3,y^4,x^2*y^2],[y,x]]]
     [440] dsolv_dual([y^2-x^3,x^2*y^2],[x,y]);
     [x*y^3+1/4*x^4*y, x^2*y, x*y^2+1/12*x^4, y^3+x^3*y,
      x^2, x*y, y^2+1/3*x^3, x, y, 1]

     [441] dsolv_test_dual();
       Output is  omitted.

