2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/116343We study the regularity of the "free surface" in boundary obstacle problems. We show that near a non-degenerate point the free boundary is a $C^{1,α}$ $(n-2)$-dimensional surface in $\real^{n-1}$.11 pages, AMSLaTeXAnalysis of PDEs35R35text