Bolyai–Gerwien theorem
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In geometry, the Bolyai–Gerwien theorem states that if two simple polygons of equal area are given, one can cut the first into finitely many polygonal pieces and rearrange the pieces to obtain the second polygon.
"Rearrangement" means that one may apply a translation and a rotation to every polygonal piece.
Unlike the solution to Tarski's circle-squaring problem, the axiom of choice is not required for the proof, and the decomposition and reassembly can actually be carried out "physically".
[edit] Higher dimensions
The analogous statement about polyhedra in three dimensions, known as Hilbert's third problem, is false, as proven by Max Dehn in 1900, leading to the Banach–Tarski paradox 24 years later.
[edit] History
Farkas Bolyai, father of Janos Bolyai, first formulated the question. Gerwien proved the theorem in 1833, but in fact Wallace had proven the same result already in 1807.
According to other sources, Farkas Bolyai and Gerwien had independently proved the theorem in 1833 and 1835, respectively.
