On a surface in Euclidean three-space, straightest paths, those of locally-shortest length, are called "geodesics." Kuen's surface has "Gaussian curvature" equal to -1 (away from curves where the surface pinches to a sharp edge). Concretely, for every geodesic triangle on the surface, the sum of the interior angles (in radians) is equal to pi minus the area of the triangle.
Printed on high-quality 170 gsm poster paper with a satin finish.
