2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/75113Cubic bipartite graphs with girth at least 6 correspond to symmetric combinatorial (v_3) configurations. In 1887 V. Martinetti described a simple reduction method which enables one to reduce each combinatorial (v_3) configuration to one from the infinite set of so-called irreducible configurations. The aim of this paper is to show that a slightly extended set of reductions enables one to reduce each combinatorial (v_3) configuration either to the Fano configuration or to the Pappus configuration.Combinatorics05C62, 05C85, 05R05, 68R10text