2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/223747We consider the Laplacian in a straight strip, subject to a combination of Dirichlet and Neumann boundary conditions. We show that a switch of the respective boundary conditions leads to a Hardy inequality for the Laplacian. As a byproduct of our method, we obtain a simple proof of a theorem of Dittrich and Kriz.12 pages, LaTeX with 4 EPS figuresMathematical PhysicsSpectral Theory35P99 (Primary) 34L15, 81Q10 (Secondary)text