></span> <span>&#45;&gt;</span> <span><span class="type-var">'a</span> list</span> <span>&#45;&gt;</span> <span><span class="type-var">'a</span> list</span></code></dt><dd><p>like filter, but returns the original list if unchanged</p></dd></dl><dl><dt class="spec value" id="val-remove_irrelevant_duplicates"><a href="#val-remove_irrelevant_duplicates" class="anchor"></a><code><span class="keyword">val</span> remove_irrelevant_duplicates : <span>equal:<span>(<span class="type-var">'a</span> <span>&#45;&gt;</s