“…As for the completeness questions, the reader is probably aware of a rich literature concerning this topic. To name just a few: there is the pioneering Isbell paper [14], then Kříž [17], Banaschewski [2,3], Banaschewski and Pultr [6,7,8], Pultr and Tozzi [25], Banaschewski, Hong and Pultr [4], Hong and Kim [13]. Extending the topic to the non-symmetric case opened new vistas and brought more understanding to some of the aspects (Frith and Hunsaker [11], Frith, Hunsaker and Walters-Wayland [12], Kim [16]).…”