Rigidity and Frobenius Structure

Abstract

We show that an irreducible ordinary differential equation on the projective line has a Frobenius structure for a power of some prime p if it is rigid in the sense of Katz and satisfies some other reasonable (and necessary) conditions relative to the prime p.

arXiv comment10 pages. The proofs of proposition 1, theorem 3 and some other brief passages have been rewritten for clarity. A few misprints were corrected