Past exam of the mathematics course of the University of Cambridge 2005 iii Paper 86 3 Solution Created 2026-10-03 Updated 2026-10-14
For a nonconstant meromorphic map, write in the usual normalization, where . Let count -points with their local degrees, and let count each distinct point once, using the same integrated logarithmic weights. At infinity the local degree is the pole order. The Nevanlinna deficiency and Nevanlinna ramification index areThe latter is an asymptotic excess-multiplicity index, not the integer local ramification degree. The Nevanlinna first main theorem gives and identifies deficiency with the lower limiting normalized proximity. The target ranges over the Riemann sphere, not just the real line.
To obtain the rational-composition growth, represent the nonconstant degree- sphere map by relatively prime homogeneous polynomials of degree . Their joint norm on the unit sphere in has a positive minimum and finite maximum: simultaneous vanishing would contradict relative primeness on the projective line. Homogeneity therefore gives constants withApply this to the entire nonvanishing lift . The logarithmic joint norm differs from by a bounded function. Its circular mean minus the value at zero is the spherical characteristic. It differs from the ordinary characteristic by : Jensen's formula applied to the entire denominator counts its zeros, whilecontrols the proximity replacement. If the denominator vanishes at zero, factor its zero and use its leading coefficient in Jensen's formula; the discrepancy is still a basepoint-dependent constant. This proves the rational composition law for the Nevanlinna characteristic here and givesIf is constant, and its characteristic is bounded instead.
For a simultaneous nonzero deficiency and ramification example choosea degree-three polynomial composed with the exponential. Its characteristic is . Its only zeros are , , all of multiplicity two. The number of distinct such points in a large disc is , so integration of their count givesThe origin contribution is handled by its usual logarithmic counting term. ThereforeThis is simultaneous deficiency and ramification for an exponential polynomial: the missing exponential value contributes a deficit, while the attained value is attained with double multiplicity.
The rational composition law for the Nevanlinna characteristic gives . Its zeros are precisely , all of multiplicity two, so and . Hence both its Nevanlinna deficiency and Nevanlinna ramification index at zero equal one third.