The Minkowski sum of two identical squares is a square whose edge is the double of the original edges.
Luca Antonelli (<a href="//commons.wikimedia.org/wiki/User:Luke_Antony" class="mw-redirect" title="User:Luke Antony">Luke Antony</a>)
CC BY-SA 3.0
<span class="int-own-work" lang="en">Own work</span>