1. I.I. Parovichenko, On the Weight and Cardinality of H-Closed Spaces [in Russian], Dokl. AN SSSR,138, No. 6, 1295–1297 (1961).
2. V. Gol'shtinskii, Addition Theorems for the Weight of Topological Spaces [in Russian], Dokl. AN SSSR,151 No. 5, 1018–1020 (1963).
3. M. Katetov, On H-Closed Extensions of Topological Spaces, Casopis mat. fys.,72, 17–32 (1947).