Show that, if E1,E2,F1,F2 are four modules over a commutative ring
C, the canonical homomorphism (21) (no. 4) is composed of the homomorphisms
Hom(E1,F1)⊗Hom(E2,F2)→Hom(E1,F2⊗Hom(E2,F2))→Hom(E1,Hom(E2,F1⊗F2))→Hom(E1⊗E2,F1⊗F2) where the first two homomorphisms come from the canonical homomorphism (7) (no. 2) and the last is the isomorphism of no. 1, Proposition 1.