Covariance of WDVV equations

The (generalized) WDVV equations for the prepotentials in 2d topological and 4,5d Seiberg-Witten models are covariant with respect to non-linear transformations, described in terms of solutions of associated linear problem. Both time-variables and the prepotential change non-trivially, but period matrix (prepotentialʹs second derivatives) remains intact.