2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/76389We compute the number of all rhombus tilings of a hexagon with sides $a,b+1,c,a+1,b,c+1$, of which the central triangle is removed, provided $a,b,c$ have the same parity. The result is a product of four numbers, each of which counts the number of plane partitions inside a given box. The proof uses nonintersecting lattice paths and a new identity for Schur functions, which is proved by means of the minor summation formula of Ishikawa and Wakayama. A symmetric generalization of this identity is stated as a conjecture.21 pages, AmS-TeX, uses TeXDrawCombinatorics05A15 05A17 05A19 05B45 05E05 52C20text