Regarding Equitable Colorability Defect of Hypergraphs

TL;DR

This paper investigates the bounds of the equitable colorability defect in hypergraphs, proving that certain inequalities involving these bounds cannot be improved by replacing specific parameters with larger values.

Contribution

It demonstrates that the inequality involving the equitable colorability defect cannot be strengthened by increasing the parameter beyond a certain point.

Findings

The inequality involving the equitable colorability defect is tight.

Replacing the parameter with a larger value does not hold in the inequality.

The relation between ecd and cd is used to establish the result.

Abstract

\noindent Azarpendar and Jafari in 2020 proved the following inequality $$\chi \left( {\rm KG} ^r ({\cal F} , s) \right) \geq \left\lceil \frac{ {\rm ecd}^r \left( {\cal F} , \left\lfloor \frac{s}{2} \right\rfloor \right) }{r-1} \right\rceil ,$$ and noted that it is plausible that the above inequality remains true if one replaces $\left\lfloor \frac{s}{2} \right\rfloor$ with $s$. \noindent In this paper, considering the relation ${\rm ecd}^r \left( {\cal F} , x \right) \geq {\rm cd}^r \left( {\cal F} , x \right)$ which always holds, we show that even in the weaker inequality $$\chi \left( {\rm KG} ^r ({\cal F} , s) \right) \geq \left\lceil \frac{ {\rm cd}^r \left( {\cal F} , \left\lfloor \frac{s}{2} \right\rfloor \right) }{r-1} \right\rceil ,$$ no number $x$ greater than $\left\lfloor \frac{s}{2} \right\rfloor$ could be replaced by $\left\lfloor \frac{s}{2} \right\rfloor$.