de Bruijn's theorem

Etymology
Devised by the Dutch mathematician Nicolaas Govert de Bruijn in a 1969 paper.

Proper noun

 * 1)  A theorem about packing congruent rectangular bricks into larger rectangular boxes so that no space is left over. It states that a "harmonic brick" (one in which each side length is a multiple of the next smaller side length) can only be packed into a box whose dimensions are multiples of the brick's dimensions.