Two New Contributions to the Three-dimensional Hardy-Hilbert-type Integral Inequalities

The Hardy-Hilbert integral inequality is one of the most celebrated results in mathematical analysis, inspiring numerous variants and extensions. In this paper, we further advance the study of three-dimensional Hardy-Hilbert-type integral inequalities by proving two new theorems. One of these is notable for its inclusion of a maximum function, a feature rarely encountered in this three-dimensional context. The associated constant factors are determined explicitly and detailed proofs are provided, without recourse to special functions.