Two Groups and are said to be isoclinic if there are isomorphisms and , where is the Center of the group, which identify the two commutator maps.
Conway, J. H.; Curtis, R. T.; Norton, S. P.; Parker, R. A.; and Wilson, R. A. ``Isoclinism.'' §6.7 in
Atlas of Finite Groups: Maximal Subgroups and Ordinary Characters for Simple Groups. Oxford, England:
Clarendon Press, pp. xxiii-xxiv, 1985.