A typical keyhole contour, used for contour integration.
Traced by <a href="//commons.wikimedia.org/wiki/User:Stannered" title="User:Stannered">User:Stannered</a>
2008-01-01
Based on <a href="https://en.wikipedia.org/wiki/Image:Keyhole_contour.png" class="extiw" title="en:Image:Keyhole contour.png">en:Image:Keyhole contour.png</a>