View source for Perfectly-normal space

A [[Normal space|normal space]] in which every closed subset is a <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/p/p072/p072120/p0721201.png" />-set (cf. [[Set of type F sigma(G delta)|Set of type <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/p/p072/p072120/p0721202.png" /> (<img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/p/p072/p072120/p0721203.png" />)]]).

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====References====
<table><TR><TD valign="top">[a1]</TD> <TD valign="top">  E. Čech,   "Topological spaces" , Interscience  (1966)  pp. 532</TD></TR></table>