Inputs a ZG-resolution R, a ZG'-resolution S, and a group homomorphism f : G ⟶ G'. It outputs a component object M with the following components.

• M!.source is the resolution R.

• M!.target is the resolution S.

• M!.mapping(w,n) is a function which gives the image in S_n, under a chain map induced by f, of a word w in R_n. (Here R_n and S_n are the n-th modules in the resolutions R and S.)

• F!.properties is a list of pairs such as ["type", "equivariantChainMap"].

The resolution S must have a contracting homotopy.