ARTIST BIO 

Henry Segerman received his masters in mathematics from the University of Oxford, and his Ph.D. in mathematics from Stanford University. He 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".

15+4 puzzle:

This variant of the classic 15 puzzle differs in the addition of four extra tiles, jammed into the puzzle by replacing the usual 4×4 frame with five 2×2 squares, hinged around a central vertex. A tile can slide across the hinge between two squares when there is no angle between them. The puzzle has a cone point with angle 5π/2 in the center. A consequence of this point of negative curvature is that the puzzle has non-trivial holonomy: a tile that travels around the central point comes back rotated by a quarter turn. Thus the orientation of the tiles is important.