Ahlfors theory

Etymology
Named after Finnish mathematician (1907—1996), who published the theory in 1935.

Noun

 * 1)  A geometric counterpart to Nevanlinna theory that extends the applicability of the concept of covering surface (of a topological space) by defining a covering number (a generalised "degree of covering") applicable to any bordered Riemann surface equipped with a conformal Riemannian metric.