2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/36152We give a short historical review of early Kaluza-Klein theories. We study various causal structures on manifolds, especially those which cannot be described by a metric tensor with signature (+---). The smooth structure (atlas) on a manifold is found to be related with its causal structure.20 pages, PostScriptGeneral Relativity and Quantum Cosmologytext