Here's some "share-and-repair"-ware written in Maple to implement
multiplications of polynomials in x and y, subject to the
commutation rule yx=qxy.
<pre>
# Multiply polynomials
pmult := proc(F,G) local flist, glist, i, j, gather;
if type(F,`+`) then flist := [op(F)] else flist := [F]; fi;
if type(G,`+`) then glist := [op(G)] else glist := [G]; fi;
gather := 0;
for i from 1 to nops(F) do
for j from 1 to nops(G) do
gather := gather + mmult(flist[i],glist[j]); od; od;
gather; end;

# Multiply monomials
mmult := proc(S,T) local sx, sy, sc, tx, ty, tc;
sx := degree(S,x);
sy := degree(S,y);
sc := simplify(S/x^sx/y^sy);
tx := degree(T,x);
ty := degree(T,y);
tc := simplify(T/x^tx/y^ty);
simplify(sc*tc*q^(sy*tx)*x^(sx+tx)*y^(sy+ty)); end;
</pre>
If you find bugs, let me know!
<p>
Jim