Order Embedding into Image is Isomorphism

Theorem
Let $\left({S, \preceq_1}\right)$ and $\left({T, \preceq_2}\right)$ be posets.

Let $S\,'$ be the image of a mapping $\phi: \left({S, \preceq_1}\right) \to \left({T, \preceq_2}\right)$.

Then $\phi$ is an order embedding from $\left({S, \preceq_1}\right)$ into $\left({T, \preceq_2}\right)$ iff $\phi$ is an order isomorphism from $\left({S, \preceq_1}\right)$ into $\left({S\,', \preceq_2 \restriction_{S\,'}}\right)$.

Proof
Let $\phi$ be an order embedding from $\left({S, \preceq_1}\right)$ into $\left({T, \preceq_2}\right)$.

Then $\phi$ is an injection into $\left({T, \preceq_2}\right)$ by definition.

From Surjection iff Image equals Codomain, any mapping from a set to the image of that mapping is a surjection.

Thus the surjective restriction of $\phi$ onto $S\,'$ is an order embedding which is also a surjection.

Hence the result from Order Isomorphism is Surjective Order Embedding.