1.2.44 `sm1.ecartd_reduction'
-----------------------------

sm1.ecartd_reduction(F,A)
     :  It returns a reduced form of F in terms of A by using  a
     tangent cone algorithm. h[0,1](D)-homogenization is used.
Example:

      input
        F=[2*(1-x-y)*dx+h,2*(1-x-y)*dy+h]$
        FF=[F,"x,y",[[dx,1,dy,1],[x,-1,y,-1]]]$
        sm1.ecartd_reduction(dx+dy,FF);

