2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/152966A set partition technique that is useful for identifying wires in cables can be recast in the language of 0--1 matrices, thereby resolving an open problem stated by R.~L. Graham in Volume 1 of this journal. The proof involves a construction of 0--1 matrices having row and column sums without gaps.Combinatoricstext