Inverse of Order Isomorphism is Order Isomorphism

Theorem
Let $$\left({S; \le_1}\right)$$ and $$\left({T; \le_2}\right)$$ be posets.

Let $$\phi$$ be a bijection from $$\left({S; \le_1}\right)$$ to $$\left({T; \le_2}\right)$$.

Then $$\phi: \left({S; \le_1}\right) \to \left({T; \le_2}\right)$$ is an isomorphism iff $$\phi^{-1}: \left({T; \le_2}\right) \to \left({S; \le_1}\right)$$ is also an isomorphism.

Proof
Follows directly from the definition of isomorphism of posets.