arguments: f g >> f*g:
Multiply f and g. If f and g are free modules, then the result is the tensor product. [type,f,type g] = [ringelem,vector], [vector,ringelem], [ringelem,matrix], [matrix,matrix], [matrix,vector], [monideal, monideal], [monomial,monomial], [ringelem, ringelem], [freemodule, freemodule].