Local properties of self-dual harmonic 2-forms on a 4-manifold

We prove a Moser-type theorem for self-dual harmonic 2-forms on closed 4-manifolds, and use it to classify local forms on neighborhoods of singular circles on which the 2-form vanishes. Removing neighborhoods of the circles, we obtain a symplectic manifold with contact boundary?we show that the contact form on each S¹ × S², after a slight modification, must be one of two possibilities.