Concerning bitopological \(QHC\) extensions (Q1917704)

The paper contains some results concerning one-point pairwise QHC-extensions of non pairwise QHC-spaces. The results are based on the following notions. A space \((X, \tau_1, \tau_2)\) is called \(ij\)-locally pairwise QHC-space if every point of \(X\) has \(\tau_j\)-open neighbourhood \(U\) such that \(\tau_i\text{-cl} U\) is an \(ij\)-\(H\)-set in \((X, \tau_1, \tau_2)\) [the third author with \textit{G. K. Banerjee} and \textit{S. Malakar}, ibid. 21, 639-648 (1990; Zbl 0711.54022)]. A space \((X, \tau_1, \tau_2)\) is called pairwise locally QHC-space if it is both 12-locally pairwise QHC-space and 21-locally pairwise QHC-space.