2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/152431For a wide class of pairs of unbounded selfadjoint operators with bounded commutator we construct a K-theoretical integer invariant which is continuous, is equal to zero for commuting operators and is equal to one for the pair (x, i d/dx).9 pages, LaTeX, version 2.09, no figuresFunctional Analysistext