Increasing Mapping Preserves Upper Bounds

Theorem
Let $L = \left({S, \preceq}\right)$, $L' = \left({S', \preceq'}\right)$ be ordered sets.

Let $f:S \to S'$ be an increasing mapping.

Let $x \in S$, $X \subseteq S$ such that
 * $x$ is upper bound for $X$.

Then $f\left({x}\right)$ is upper bound for $f\left[{X}\right]$.

Proof
Let $y \in f\left[{X}\right]$.

By definition of image of set:
 * $\exists z \in X: y = f\left({z}\right)$

By definition of upper bound:
 * $z \preceq x$

Thus by definition of increasing mapping:
 * $y \preceq' f\left({x}\right)$