Abstract. We show that in a finite semimodular lattice, the ordering of join-irreducible congruences is done in a special type of sublattice, we call a tight $S_7$.
AMS Subject Classification
(1991): 06C10, 06B10
Keyword(s):
Semimodular lattice,
planar,
congruence,
prime interval
Received April 21, 2007, and in final form January 31, 2008. (Registered under 6001/2009.)
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