The period map and the discriminant

Nondegeneracy and compatibility is proved for the period map on the strata of the discriminant of a versal deformation of a critical point of a function (under hypotheses indicated in the paper). The weight foliation on the discriminant of a versal deformation of $A_4$ is described. The singularities of the foliation are connected with the singularities of the degeneration of the symplectic structure on a four-dimensional manifold.
Figures: 10.
Bibliography: 30 titles.