  We offer a derivation of the duality between the topological U(1) gauge
theory on a Calabi-Yau 3-fold and the topological A-model on the same manifold.
This duality was conjectured recently by Iqbal, Nekrasov, Okounkov, and Vafa.
We deduce it from the S-duality of the IIB superstring. We also argue that the
mirror version of this duality relates the topological B-model on a Calabi-Yau
3-fold and a topological sector of the Type IIA Little String Theory on the
same manifold.
