Hyperheavenly spaces and their application in Walker and para-K\"ahler geometries: Part I

Abstract

Spaces equipped with congruences of null strings are considered. A special attention is paid to the spaces which belong to the two-sided Walker class and para-K\"ahler class. Properties of an intersection of self-dual and anti-self-dual congruences of null strings are used as an additional criterion for a classification of such spaces. Finally, a few examples of para-K\"ahler and para-K\"ahler-Einstein spaces are presented.