Illustration of <a href="https://en.wikipedia.org/wiki/Monotonic_function" class="extiw" title="en:Monotonic function">en:Monotonic function</a>
<a href="//commons.wikimedia.org/wiki/User:Oleg_Alexandrov" title="User:Oleg Alexandrov">Oleg Alexandrov</a>
self-made with <a href="https://en.wikipedia.org/wiki/Inkscape" class="extiw" title="en:Inkscape">en:Inkscape</a>