  Extensions of a direct product T of two cyclic groups Z_n1 and Z_n2 by an
Abelian (gauge) group G with the trivial action of T on G are considered. All
possible (nonequivalent) factor systems are determined using the Mac Lane
method. Some of resulting groups describe magnetic translation groups. As
examples extensions with G=U(1) and G=Z_n are considered and discussed.
