1 The coefficients of the Seiberg - Witten prepotential as intersection numbers ( ? ) ∗

The n-instanton contribution to the Seiberg-Witten prepotential of N = 2 supersymmetric d = 4 Yang Mills theory is represented as the integral of the exponential of an equivariantly exact form. Integrating out an overall scale and a U(1) angle the integral is rewritten as (4n − 3) fold product of a closed two form. This two form is, formally, a representative of the Euler class of the Instanton moduli space viewed as a principal U(1) bundle, because its pullback under bundel projection is the exterior derivative of an angular one-form. We comment on a recent speculation of Matone concerning an analogy linking the instanton problem and classical Liouville theory of punctured Riemann spheres. ∗ To be published in the collection “From Integrable Models to Gauge Theories” (World Scientific, Singapore, 02 ) to honour Sergei Matinyan at the occasion of his 70’th birthday. ♭ on leave of absence from Yerevan Physics Institute, Armenia e-mail: [email protected] [email protected] [email protected]