Pythagorean Theorem

__Pythagorean Theorem:__
In a right angled triangle: the square of the hypotenuse is equal to the sum of the squares of the other two sides.

If two polygons have the same area, then they are decomposable in the same set of polygons.

That is, if two polygons have equal areas, then any of them can be decomposed into a finite set of pieces with which it is possible to reconstruct exactly the other polygon.