Research Problems in Function Theory — Problem 1.31

Definitions and mathematical statement

Shared notation.

$\mathbb N=\{1,2,\ldots\}$, and $\mathbb Z,\mathbb Q,\mathbb R,\mathbb C$ denote the integers, rationals, reals and complex numbers. Any other conventions are specified locally.

For a nonconstant meromorphic function $f$ on $\mathbb C$, let $n(r,a,f)$ count the solutions of $f(z)=a$ in $|z|\le r$, with multiplicity; $a=\infty$ counts poles. Let $\bar n$ count each point once. The integrated count is \[ N(r,a,f)=n(0,a,f)\log r+\sum_{0<|z|\le r,\ f(z)=a}\log(r/|z|), \] where the sum repeats each point according to multiplicity; $\bar N$ has the same formula without repetitions. Write $\log^+x=\max(\log x,0)$ and \[ m(r,\infty,f)=\frac1{2\pi}\int_0^{2\pi}\log^+|f(re^{it})|\,dt,\quad m(r,a,f)=\frac1{2\pi}\int_0^{2\pi}\log^+\frac1{|f(re^{it})-a|}\,dt\quad(a\in\mathbb C). \] The Nevanlinna characteristic is $T(r,f)=m(r,\infty,f)+N(r,\infty,f)$. Its order and lower order are \[ \rho(f)=\limsup_{r\to\infty}\frac{\log T(r,f)}{\log r},\qquad \lambda(f)=\liminf_{r\to\infty}\frac{\log T(r,f)}{\log r}. \] The deficiency is $\delta(a,f)=1-\limsup_{r\to\infty}N(r,a,f)/T(r,f)$, and the reduced-count index is $\Theta(a,f)=1-\limsup_{r\to\infty}\bar N(r,a,f)/T(r,f)$. A value is deficient if $\delta(a,f)>0$. An entire function is holomorphic on all of $\mathbb C$; for an entire function, $M(r,f)=\max_{|z|=r}|f(z)|$.

For angles $\theta$ modulo $2\pi$ and $0<\varepsilon<\pi$, put \[ D(\theta,\varepsilon)=\{z\ne0:\min_{j\in\mathbb Z}|\arg z-\theta+2\pi j|<\varepsilon\}. \] Saying that $f$ assumes $a$ infinitely often in this sector means that the equation $f(z)=a$ has infinitely many distinct solutions there, with poles interpreted as $\infty$-points.

Statement recorded in the supplied source.

For every transcendental meromorphic function $f$ in the plane, does there exist $\theta_0$ such that, for every $\varepsilon>0$ sufficiently small, at least one of the following holds in $D(\theta_0,\varepsilon)$?

1. $f$ assumes every finite value infinitely often.
2. For every integer $k\ge1$, $f^{(k)}$ assumes every value of $\mathbb C\setminus\{0\}$ infinitely often.

Here transcendental means not rational. If this property cannot be proved for all such $f$, does it hold under the weaker growth assumption $T(r,f)/(\log r)^2\to\infty$? The known theorem assumes $T(r,f)/(\log r)^3\to\infty$. The disjunction is inside the quantifier over sector widths. [S2]

Short English statement

Remove the cubic logarithmic growth condition from the directional value-distribution theorem, or replace it by its quadratic counterpart, preserving the original alternative about all derivatives. [S2]

Sources

• S1 ULAM.AI and the UnsolvedMath Contributors, UnsolvedMath: A Curated Collection of Open Mathematics Problems, record 2301031 (AMR-022-1031). CC BY 4.0. https://huggingface.co/datasets/ulamai/UnsolvedMath.
• S2 Walter K. Hayman and Eleanor F. Lingham, Research Problems in Function Theory, Fiftieth Anniversary Edition (2018), arXiv:1809.07200. Problem 1.31, its full Update 1.31, and chapter notation; original author TeX. https://arxiv.org/abs/1809.07200.