Bruck-Ryser-Chowla theorem

Etymology
Named after Richard Bruck, H. J. Ryser, and Sarvadaman Chowla.

Proper noun

 * 1)  A result on the combinatorics of block designs, stating that, if a (v, b, r, k, λ)-design exists with v = b (a symmetric block design), then: (i) if v is even, then k &minus; λ is a square; (ii) if v is odd, then the following Diophantine equation has a nontrivial solution: x2 &minus; (k &minus; λ)y2 &minus; (&minus;1)(v&minus;1)/2 λ z2 = 0.