Computes the dual group G * of G and a map M from G x G * to Z/mZ for m the exponent of G that allows G * to act on G. The group G must be finite.
Computes H := H2(G, Q/Z) and a map f : H to (G x G to Z/mZ) that will give the cocycles as maps from G x G to Z/mZ, m := #G.
For a subgroup U of G and H2 = H2(G, Q/Z) computes H2(U, Q/Z) in a compatible way together with the restriction map into H2.The abelian group H2 must be the result of H2_G_QmodZ as this function relies on the attributes stored in there.