There are three versions of the conjecture, one in terms of logarithmically convex functions, one in terms of increasing functions, and one in terms of non-negative functions. The conjecture has implications in the study of complex functions and is related to Euler's Beta function. While the conjecture is known to hold for certain conditions, counterexamples have also been found.
The first statement in terms of logarithmically convex functionsedit
Khabibullin's conjecture (version 1, 1992). Let be a non-negative increasing function on the half-line such that . Assume that is a convex function of . Let , , and . If
(1)
then
(2)
This statement of the Khabibullin's conjecture completes his survey.[2]
Relation to Euler's Beta functionedit
The product in the right hand side of the inequality (2) is related to the Euler's Beta function:
The Khabibullin's conjecture is valid for without the assumption of convexity of . Meanwhile, one can show that this conjecture is not valid without some convexity conditions for . In 2010, R. A. Sharipov showed that the conjecture fails in the case and for .[3]
The second statement in terms of increasing functionsedit
Khabibullin's conjecture (version 2). Let be a non-negative increasing function on the half-line and . If
then
The third statement in terms of non-negative functionsedit
Khabibullin's conjecture (version 3). Let be a non-negative continuous function on the half-line and . If
^Khabibullin B.N. (1999). "Paley problem for plurisubharmonic functions of finite lower order". Sbornik: Mathematics. 190 (2): 309–321. Bibcode:1999SbMat.190..309K. doi:10.1070/SM1999v190n02ABEH000387. S2CID 250806401.
^Khabibullin BN (2002). "The representation of a meromorphic function as the quotient of entire functions and Paley problem in : a survey of some results". Mat. Fizika, Analiz, Geometria. 9 (2): 146–167. arXiv:math.CV/0502433.
^Sharipov, R. A. (2010). "A Counterexample to Khabibullin's Conjecture for Integral Inequalities". Ufa Mathematical Journal. 2 (4): 99–107. arXiv:1008.2738. Bibcode:2010arXiv1008.2738S.