The Tits group "T" is sometimes also regarded as a sporadic group (it is almost but not strictly a group of Lie type), which is why in some sources the number of sporadic groups is given as 27 instead of 26. In some other sources, the Tits group is regarded as neither sporadic nor of Lie type. Anyway, it is the of the "infinite" family of commutator groups — and thus "per definitionem" not sporadic. For these finite simple groups coincide with the groups of Lie type But for the derived subgroup , called Tits group, is simple and has an index 2 in the finite group of Lie type which —as the only one of the whole family— is not simple.