Let $A$ be a retract of $X$. Show that if $i:A\to X$ is the inclusion operator , then $i_*:H_n(A) \to H_n(X)$ is an isomorphism
(It's easy to see that it's a monomorphism. But why is it an epimorphism?)
Thanks!
Let $A$ be a retract of $X$. Show that if $i:A\to X$ is the inclusion operator , then $i_*:H_n(A) \to H_n(X)$ is an isomorphism
(It's easy to see that it's a monomorphism. But why is it an epimorphism?)
Thanks!