Subset Product with Identity

Theorem
Let $\struct {S, \circ}$ be a magma.

Let $\struct {S, \circ}$ have an identity element $e$.

Then $e \circ S = S \circ e = S$, where $\circ$ is understood to be the subset product with singleton.

Proof
Thus:
 * $e \circ S = S$

A similar argument shows that:
 * $S \circ e = S$