How to show that the groups $(Z_4, +_4)$ and $(Z_5, ・_5)$ are isomorphic? [on hold]

I am doing CLRS exercise 31.3-1.

The question is to show that these groups $ (Z_4, +_4)$ and $ (Z_5, ・_5)$ are isomorphic by exhibiting a one-to-one correspondance α between their elements such that $ a + b ≡ c $ (mod 4) if and only if $ α(a)・α(b)≡α(c)$ (mod 5).

I understand that we have the following tables:

$ (Z_4, +_4)$

    0   1   2   3 0   0   1   2   3 1   1   2   3   4 2   2   3   0   1 3   3   0   1   2  

$ (Z_5, ・_5)$

    1   2   3   4 1   1   2   3   4 2   2   4   1   3 3   3   1   4   2 4   4   3   2   1   

But what does it mean to find isomorphic relationships between these two tables?