Menger conjectured that subsets of $mathbb R$ with the Menger property must be $sigma$-compact. While this is false when there is no restriction on the subsets of $mathbb R$, for projective subsets it is known to follow from the Axiom of Projective Determinacy, which has considerable large cardinal consistency strength. We show that the perfect set version of the Open Graph Axiom for projective sets of reals, with consistency strength only an inaccessible cardinal, also implies Mengers conjecture restricted to this family of subsets of $mathbb R$.
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