Multiplicative Group of Reduced Residues Modulo 8 is Klein Four-Group

Theorem
Let $K_4$ denote the Klein $4$-group.

Let $R_4$ be the multiplicative group of reduced residues Modulo $8$.

Then $K_4$ and $R_4$ are isomorphic algebraic structures.

Proof
Establish the mapping $\phi: K_4 \to R_4$ as follows:

From Isomorphism by Cayley Table, the two Cayley tables can be compared by eye to ascertain that $\phi$ is an isomorphism:

Cayley Table of Klein $4$-Group
The Cayley table for $K_4$ is as follows:

Multiplicative Group of Reduced Residues Modulo $8$
The Cayley table for $S$ is as follows: