# Exceptional value

A concept in value-distribution theory. Let be a meromorphic function in the whole -plane and let denote its number of -points (counting multiplicities) in the disc . According to R. Nevanlinna's first fundamental theorem (cf. [1]), as ,

where is the characteristic function, which does not depend on , is the counting function (the logarithmic average of ) and is a function expressing the average proximity of the values of to on (cf. Value-distribution theory). For the majority of values the quantities and are asymptotically equivalent, as . A (finite or infinite) number is called an exceptional value if this equivalence as is violated. One distinguishes several kinds of exceptional values.

A number is called an exceptional value of in the sense of Poincaré if the number of -points of in the whole plane is finite (cf. [1], [2]), in particular if for any .

A number is called an exceptional value of in the sense of Borel if grows slower, in a certain sense, than , as (cf. [1], [2]).

A number is called an exceptional value of in the sense of Nevanlinna (cf. [1]) if its defect (cf. Defective value)

A number is called an exceptional value of in the sense of Valiron if

A number for which

is also called an exceptional value for . The quantity (the positive deviation of ) characterizes the rate of the asymptotic approximation of to (cf. [3]).

#### References

[1] | R. Nevanilinna, "Analytic functions" , Springer (1970) (Translated from German) |

[2] | A.A. Gol'dberg, I.V. Ostrovskii, "Value distribution of meromorphic functions" , Moscow (1970) (In Russian) |

[3] | V.P. Petrenko, "Growth of meromorphic functions of finite lower order" Math. USSR Izv. , 3 : 2 (1969) pp. 391–432 Izv. Akad. Nauk SSSR Ser. Mat. , 33 : 2 (1969) pp. 414–454 |

#### Comments

An -point of is a point such that .

**How to Cite This Entry:**

Exceptional value.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=Exceptional_value&oldid=18994