Talk:Zassenhaus lemma

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I added a condition that B and D are normal subgroups of A and C, using the usual triangle notation. I'd be surprised if this is not a necessary condition for the conclusion to hold. Please correct if original formulation was actually correct.

Perhaps the article should explicitly state in words which subgroups are normal subgroups of others. For example, one of the conclusions of the lemma is that is a normal subgroup of (which is currently implicit in the notation because of the quotient notation). Saying this in words provides somebody learning group theory a way to look up the meaning, of say normal subgroup, elsewhere in wikipedia, which notation is not as convenient for.

Although it's rather obvious, the article could emphasize that the butterfly showing the Hasse diagram is upside down in the sense that smaller subgroups are higher. DRLB (talk) 15:42, 9 April 2008 (UTC)