Another answer was given by Aarts and De Groot in Complete regularity as a separation axiom Canadian Journal of Mathematics 21 1969 96–105. Frink's condition sets things up for a proof a la Urysohn's Lemma; Aarts and De Groot' condition is in terms of subbases and the proof proceeds by constructing a Hausdorff compactification.
KP Hart
- 11.4k
- 38
- 48