Vol 26(4) (2019) #P4.45 — Comment by the authors, 3 July 2024.
Our Theorem 7 states that for positive integers m, n with m ≤ n,
γ(Qm×n ) ≥ min{m,⌈(m+n-2)/4⌉}.
We note that, with m ≤ n,
γ(Qm×n) ≥ min{m-1,
⌈(m+n-2)/4⌉} was proved in the paper "On bounds for a
covering problem" by V. Raghavan and V. M. Venketesan,
Inform. Process. Lett. 25:281-284, 1987.