On codes in the projective linear group $PGL(2,q)$

Abstract

In this paper, we resolve a conjecture of Green and Liebeck [Disc. Math., 343 (8):117119, 2019] on codes in $PGL(2,q)$. To be specific, we show that: if $D$ is a dihedral subgroup of order $2(q+1)$ in $G=PGL(2,q)$, and $A=\{g\in G:g^{q+1}=1,g^2\ne 1\}$, then $\lambda G=A\cdot D$, where $\lambda =q$ or $q-1$ according as $q$ is even or odd.