Resumen
In this paper, a new kind of set called an a?-open set is introduced and investigated using the ?-operator due to Ogata. Such sets are used for studying new types of mappings, viz. a?-continuous, a(?,ß)-irresolute, etc. Finally, new separation axioms: a?-Ti (i = 0, ½, 1, 2), a?-Di (i = 0, 1, 2), and a new notion of the graph of a function called an a?-closed graph.