2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/74970In the monograph "Axioms and Hulls" (1992) Donald Knuth studies some axiomatizations of geometric situations. The structures described by one of the axiom systems are called CC-systems. Knuth proves that it is NP-complete to decide, whether a partially defined CC-system can be extended to a complete CC-system. The aim of this note is to show that Knuth's proof of this result also implies that it is NP-complete to decide the extendability of partially defined chirotopes.4 pagesCombinatoricstext