source f
This yields the source of a map of a labeled module, as a labeled module.
i1 : S=ZZ/101[x,y,z];
i2 : F=labeledModule(S^2); o2 : free S-module with labeled basis
i3 : G=symmetricPower(2,F); o3 : free S-module with labeled basis
i4 : f=map(G,F,{{x,y},{y,z},{z,x}}) o4 = | x y | | y z | | z x | 3 2 o4 : Matrix S <--- S
i5 : source f 2 o5 = S o5 : free S-module with labeled basis
i6 : basisList source f o6 = {0, 1} o6 : List