Topology problem.?

Let B = {1, 3, 5, 7, ...}. If A = {1, 2, 3, 4, 5, 6}, universe is N and τ = {N, ∅, B, {1}, {1, 3}, {1, 3, 5}, ...}, find A^0, A^a, A with a bar over it.

My question is, what does A^a mean? I know A^0 is interior of A and A with a bar over it is closure. Buy what is A^a?

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