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; A. V. Arkhangel'skii, “Mappings and spaces”, Russian Math. Surveys, 21:4 (1966), ; V. I. Ponomarev, “On spaces co-absolute with metric spaces”, Russian Math. Surveys, 21:4 (1966), ; A. V. Arkhangel'skii, “Mappings and spaces”, Russian Math. Surveys, 21:4 (1966),