impossible object
Möbius strip – Two-dimensional surface with only one side and only one edge Non-Euclidean geometry – Two geometries based on axioms closely related to those specifying Euclidean geometry Paradox – Statement that apparently contradicts itself Puzzle – Problem or enigma that tests the ingenuity of the solver strange loop – Cyclic structure that goes through several levels in a hierarchical system. Surrealism – International cultural movement started in 1917 Tesseract – Four-dimensional analogue of the cube