One of my favorite KöMaL problems (B. 4463): "In the Four-square Round Forest, trees form a regular triangular lattice. Is it possible to build a fence around a rectangular part of the forest such that the vertices of the rectangle are lattice points and the number of lattice points on the boundary of the rectangle is the same as in the interior?"

0xDE@11011110@mathstodon.xyzSpoiler

@jsiehler Is there a trick to this? I found a solution quickly by looking at small rectangle heights and finding a width that worked for one of the heights, but I wouldn't say there was any elegance to my reasoning.