ON ACCESSIBLE CLASSES OF GROUPS AND SEMIGROUPS
Л. М. Мартынов · Mathematics of the USSR-Sbornik · 1973
In this paper it is proved that any residually complete class of groups is either 1-step accessible in the class of all groups or is not γ-step accessible for any ordinal number γ, and there is given an extensive class of varieties of semigroups which cannot be γ-step accessible in the class of all semigroups. Bibliography: 15 items.