a necker cube is an example of a(n)
Necker cube The Necker cube is an optical illusion first published as a rhomboid in 1832 by Swiss crystallographer Louis Albert Necker.[1] It is a simple wire-frame drawing of a cube with no visual cues as to its orientation, so it can be interpreted to have either the lower-left or the upper-right square as its front side. Necker cube is used in studies of human visual perception.
Optimal solutions for Rubik's Cube The maximum number of face turns needed to solve any instance of the Rubik's Cube is 20,[2] and the maximum number of quarter turns is 26.[3] These numbers are also the diameters of the corresponding Cayley graphs of the Rubik's Cube group. In STM (slice turn metric) it's unknown.