Abstract
The inequality |X|≤2χ(X) has been proved to be true for Lindelöf spaces (Arhangel'skiĭ, 1969), H-closed spaces (Dow-Porter, 1982) and ccc spaces (Hajnal-Juhász 1967), by quite different arguments. We present a common extension of all these properties which allows us to give a unified proof of these three theorems.
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