2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/218700In $\mathcal L$, the semilattice of faces of an $n$-cube, we count the number of automorphisms of $\mathcal L$ that fix a given subalgebra -- either pointwise or as a subalgebra. By using Möbius inversion we get a formula for the number of derangements on the $n$-cube in terms of the Möbius function on the lattice of MR-subalgebras. We compute this Möbius function.13 pages, minor revisions of definitionsCombinatorics06A07 (Primary), 05A18, 05E25 (Secondary)text