2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/122665We prove that pseudo-differential operators with symbols in the class $S_{1,δ}^0$ ($0<δ<1$) are not always bounded on the modulation space $M^{p,q}$ ($q\neq2$).9 pagesFunctional AnalysisAnalysis of PDEs42B35; 47G30text