Geometric dissection

thumb|300px|Like most modern sets, this wooden tangram is stored in the square configuration.

theorem that there exists a decomposition of a unit solid ball into a finite number of disjoint subsets, which can be put back together in a different way to yield two identical copies of the unit sphere

optical illusion used in mathematics

right|thumb|Ostomachion (after Suter) thumb|Ostomachion (after Suter): square reformed with some pieces turned over thumb|alt=Ostomachion Figures| Ostomachion figures mentioned by Ausonius and others (Bibliotheca Augustana)

theorem

one of twenty-three, asking whether one polyhedra can be cut and reassembled into another

mathematical problem

the problem of partitioning a given shape into pieces that can be rearranged to form a second given shape

tiling puzzle where a set of pieces can be assembled in different ways to produce two or more distinct geometric shapes

One can't dissect a square into an odd number of triangles of equal area

property of polyhedra invariant under scissors congruence

thumb|A 6-equidissection of a square

Tiling puzzle with a T shape