TITLE: Definition of $\Omega$-group and $\Omega$-composition series
QUESTION [6 upvotes]: What are the definitions of $\Omega$-group and $\Omega$-composition series? No luck searching on the internet..

REPLY [7 votes]: You are probably looking for groups with operators.  If that doesn't sound right, you might try the $\Omega$-subgroups from the theory of $p$-groups.