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Published online by Cambridge University Press: 09 April 2009
Let be an infinite r.e. repère, an infinite dimensional r.e. space such that ≦ L(). A condition is derived that is both necessary and sufficient for the existence of an infinite subset β ⊂ such that L(β)∪ is not an α-space. Examples which satisfy this condition are exhibited, proving that the class of α-spaces is not closed under intersections.