Claim:⊆ is transitive

From CS2800 wiki
If [math]A \href{/cs2800/wiki/index.php/%5Csubseteq}{\subseteq} B [/math] and [math]B \href{/cs2800/wiki/index.php/%5Csubseteq}{\subseteq} C [/math] then [math]A \href{/cs2800/wiki/index.php/%5Csubseteq}{\subseteq} C [/math]