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Une classe reguliere d'espaces de Baire. C. R. Acad. Paris, 260 (1958), 218 - 220. 
MR 0092956 | 
Zbl 0078.14903 
[3] Z. Frolík: 
Generalizations of the $G_\delta$-property of Complete Metric Spaces. Czechosl. Math. J. 10 (85), 1960, 359-379. 
MR 0116305