A <a href="https://en.wikipedia.org/wiki/polygon" class="extiw" title="en:polygon">polygon</a> discovered by <a href="https://en.wikipedia.org/wiki/Robert_Amman" class="extiw" title="en:Robert Amman">Robert Amman</a>, formed from a regular hexagon by adding projections on two of its sides and matching indentations on three sides. It may be surrounded by four layers of congruent copies of itself, but not five. See <a href="https://en.wikipedia.org/wiki/Heesch%27s_problem" class="extiw" title="en:Heesch's problem">Heesch's problem</a>.
<a href="//commons.wikimedia.org/wiki/User:David_Eppstein" class="mw-redirect" title="User:David Eppstein">David Eppstein</a>
self-made, originally for <a rel="nofollow" class="external text" href="http://www.ics.uci.edu/~eppstein/junkyard/heesch/">The Geometry Junkyard</a>; also previously uploaded to <a href="https://en.wikipedia.org/wiki/Image:Amman-Heesch-4.gif" class="extiw" title="en:Image:Amman-Heesch-4.gif">en:Image:Amman-Heesch-4.gif</a>