User:Kc kennylau/sandbox

Theorem
Let $\left({R, +, \circ}\right)$ be a ring with unity $1_R$.

Let $\left({-1}\right)_R$ be the additive inverse of $1_R$.

Then:


 * $\left({-1}\right)_R \circ \left({-1}\right)_R = 1_R$

Proof
Let $0_R$ be the ring zero of $\left({R, +, \circ}\right)$.

Then: