The Penrose triangle, (aka the Penrose tribar), is an impossible object. It was first created by Swedish artist, Oscar Reutersvärd in 1934. The mathematician Roger Penrose independently devised and popularised it in the 1950's, describing it as "impossibility in its purest form". It is featured prominently in the works of artist M. C. Escher, whose earlier depictions of impossible objects partly inspired it.

The tribar appears to be a solid object, made of three straight beams of square cross-section which meet pairwise at right angles at the vertices of the triangle they form. The beams may be broken, forming cubes or cuboids; the logo of National Westminster Bank, comprising three chevrons that form a broken hexagon, has sometimes been depicted with the chevrons as two sides of cubes forming the corners of a Penrose triangle.

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