Geodesic
On a problem of Nogura about the product of Fréchet-Urysohn $\langle \alpha_4\rangle$-spaces
Commentationes Mathematicae Universitatis Carolinae, Tome 40 (1999) no. 3, pp. 537-549.

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Assuming Martin's Axiom, we provide an example of two Fréchet-Urysohn $\langle\alpha_4\rangle$-spaces, whose product is a non-Fréchet-Urysohn $\langle\alpha_4\rangle$-space. This gives a consistent negative answer to a question raised by T. Nogura.
Classification : 03E50, 54A20, 54A35, 54B10, 54D55, 54D80, 54G15, 54G20
Keywords: Fréchet-Urysohn space; $\langle\alpha_4\rangle$-space; Martin's Axiom; almost disjoint functions; double iterated power 
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Costantini, Camillo. On a problem of Nogura about the product of Fréchet-Urysohn $\langle \alpha_4\rangle$-spaces. Commentationes Mathematicae Universitatis Carolinae, Tome 40 (1999) no. 3, pp. 537-549. http://geodesic.mathdoc.fr/item/CMUC_1999__40_3_a12/