Gong, JianhuaReilly, Ivan L.2017-06-162017-06-162007-10-011576-9402https://riunet.upv.es/handle/10251/83074[EN] The main purpose of this paper is to prove the following two theorems, an order hereditary closure preserving sum theorem and an hereditary theorem: (1) If a topological property P satisfies (Σ′) and is closed hereditary, and if V is an order hereditary closure preserving open cover of X and each V ϵ V is elementary and possesses P, then X possesses P. (2) Let a topological property P satisfy (Σ′) and (β), and be closed hereditary. Let X be a topological space which possesses P. If every open subset G of X can be written as an order hereditary closure preserving (in G) collection of elementary sets, then every subset of X possesses P.Reconocimiento - No comercial - Sin obra derivada (by-nc-nd)Elementary setOrder hereditary closure preservingSum theoremArtículo2017-06-1610.4995/agt.2007.1892Abierto1989-4147