ilter_fun" class="anchor"></a><code><span class="keyword">val</span> filter_fun : string <span>&#45;&gt;</span> <span><a href="index.html#type-t">t</a> list</span> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <span><span><a href="index.html#type-t">t</a> list</span> option</span></code></dt><dd><p>filtering function calls like (sqrt, exp, ln ...) is done here : given a function name, a list of argument, and a result, it remove points that cannot satisfy the relation : f(ar