  A-nuclei (groups of regular permutations) of a quasigroup are studied. A
quasigroup is A-nuclear if and only if it is group isotope. Any quasigroup with
permutation medial or paramedial identity is an abelian group isotope.
Definition of A-center of a quasigroup is given. A quasigroup is A-central if
and only if it is abelian group isotope. If a quasigroup is central in
Belyavskaya-Smith sense, then it is A-central. Conditions when A-nucleus define
normal congruence of a quasigroup are established, conditions normality of
nuclei of some inverse quasigroups are given. Notice, definition of A-nucleus
of a loop and A-center of a loop coincides, in fact, with corresponding
standard definition.
