Henry Segerman is an associate professor in the department of mathematics at Oklahoma State University. His research interests are in three-dimensional geometry and topology, and in mathematical art and visualization. In visualization he works in 3D printing, spherical video, virtual, and augmented reality. He is the author of the book "Visualizing Mathematics with 3D Printing".
In this variant of the 15 puzzle, every vertex has five squares around it. Neighbouring squares are connected by hinges, across which tiles can slide when the squares are flat. This can be difficult: the whole frame must be manipulated to get a hinge flat, possibly requiring many preparatory moves. The puzzle has non-trivial holonomy: sliding a tile around any vertex rotates it by a quarter turn. There are no neat rows to put the numbers in for the solved state. Instead the numbers spiral out from the center, each pointing to the number following it.