2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/54565It is argued that $M$-theory compactified on {\it any} of Joyce's $Spin(7)$ holonomy 8-manifolds are dual to compactifications of heterotic string theory on Joyce 7-manifolds of $G_2$ holonomy.14 Pages, LatexHigh Energy Physics - TheoryN=1 M-theory-Heterotic Duality in Three Dimensions and Joyce Manifoldstext