On the Borsuk–Ulam theorem for Lipschitz mappings in an infinite-dimensional space

The present paper is devoted to the study of the solvability and dimension of the solution set of the equation $A (x) = f (x)$ on the sphere of a Hilbert space, in the case when A is a closed surjective operator and f a Lipschitz odd mapping. This theorem is a certain "analogue" of the infinite-dimensional version of the Borsuk-Ulam theorem.