NEVANLINNA, Le Theoreme de Picard-Borel, 1929

First edition.
The Picard-Borel theorem refers to a set of theorems in complex analysis that relate to the question of the reach of analytic functions. Simply put, the Picard-Borel theorem states that every non-constant entire function takes on almost every complex value. The theorem was independently proved by Émile Picard and Émile Borel in the early 20th century.