Construct S polynomial using GAP.

Question

I am trying to write a function which would create an s polynomial when provided with two polynomials : p1 and p2.

Here it is :

sPolynomial := function(p1, p2, order)
    local lcm, res;

    lcm := Lcm(LeadingMonomialOfPolynomial(p1, order), LeadingMonomialOfPolynomial(p1, order));
    res := (lcm*p1)/LeadingTermOfPolynomial(p1,order) - (lcm*p2)/LeadingTermOfPolynomial(p2,order);

    return res;

end;

Then here is what I am trying to do:

gap> x := Indeterminate(FLOAT_PSEUDOFIELD,"x");
x
gap> y := Indeterminate(FLOAT_PSEUDOFIELD, "y");
y
gap> l:=[x^3-2*x*y,(x^2)*y-2*y^2+x,-x^2,-2*x*y,-2*y^2+x];
gap> lexord:=MonomialLexOrdering();
gap> Read("SPolynomial.txt");
gap> sPolynomial(l[4], l[5], lexord);
Error, no method found! For debugging hints type ?Recovery from NoMethodFound
Error, no 1st choice method found for `IsFiniteDimensional' on 1 arguments at /proc/cygdrive/C/gap-4.9.1/lib/methsel2.g:250 called from
IsFiniteDimensional( V ) at /proc/cygdrive/C/gap-4.9.1/lib/modfree.gi:120 called from
IsFinite( r ) at /proc/cygdrive/C/gap-4.9.1/lib/ringpoly.gi:172 called from
PolynomialRing( DefaultField( cfs ), ind ) at /proc/cygdrive/C/gap-4.9.1/lib/ringpoly.gi:579 called from
DefaultRingByGenerators( arg[1] ) at /proc/cygdrive/C/gap-4.9.1/lib/ring.gi:396 called from
DefaultRing( arg ) at /proc/cygdrive/C/gap-4.9.1/lib/ring.gi:1373 called from
...  at *stdin*:19
you can 'quit;' to quit to outer loop, or
you can 'return;' to continue
brk> quit;

How could it be that the method was not found? I checked that it is situated in the needed directory.

What am I doing wrong in the case? Will be grateful for any help provided.