lass="spec value" id="val-is_subtype"><a href="#val-is_subtype" class="anchor"></a><code><span class="keyword">val</span> is_subtype : <span>subtype:<a href="index.html#type-t">t</a></span> <span>&#45;&gt;</span> <span>supertype:<a href="index.html#type-t">t</a></span> <span>&#45;&gt;</span> bool</code></dt><dd><p>A is a subtype of B, if all values of A can be represented in B. Subtype relation is reflexive: everything is a subtype of itself.</p></dd></dl><dl><dt class="spec value" id="val-join"><a href="#v