Dear GAP-forum, How can I define a function with explicit domain and codomain? I need it do find the size of the kernel of the mapping t: C_4^3 \times S_4 \rightarrow \{ \pm 1 \}: (h_1,h_2,h_3,h_4) \mapsto sgn(h_1)sgn(h_2)sgn(h_3)sgn(h_4) Best regards, Inneke Van Gelder