2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/61597We compute 2-enumerations of certain halved alternating sign matrices. In one case the enumeration equals the number of perfect matchings of a halved Aztec diamond. In the other case the enumeration equals the number of perfect matchings of a halved fortress graph. Our results prove three conjectures by Jim Propp.11 pages, AmS-LaTeX, uses TeXDrawCombinatorics05A15text