## chain map

Hi, I need to help with this problem

The interval chain complex is the chain complex I defined by

0 if n > 1,
I_n = Z if n = 1
Z ⊕ Z if n = 0.

with the only nonzero boundary map given by n → (−n, n).
Show that a chain homotopy between two chain maps C → D is exactly the same
as a chain map C ⊗ I → D.

Thanks