2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/223868This note is to indicate the new sphere of applicability of the method developed by Mlak as well as by the author. Restoring those ideas is summoned by current developments concerning $K$-spectral sets on numerical ranges.Functional AnalysisSpectral TheoryPrimary 47A12, 47A25; Secondary 47A60, 46J10text