Subset of Ordinal implies Cardinal Inequality

Theorem
Let $S$ be a set.

Let $x$ be an ordinal such that $S \subseteq x$.

Then:
 * $\card S \le \card x$

where $\card S$ denotes the cardinality of $S$.

Proof
Since $x$ is an ordinal, it follows that $x \sim \card x$ by Ordinal Number Equivalent to Cardinal Number.

This satisfies the hypothesis for Subset implies Cardinal Inequality.

Therefore:
 * $\card S \le \card x$