Computing congruence lattices of finite lattices
Ralph S. Freese · Proceedings of the American Mathematical Society · 1997
An inequality between the number of coverings in the ordered set J ( C o n J ) \operatorname {J}({\mathbf {Con\;J}}) of join irreducible congruences on a lattice L \operatorname {L} and the size of L {\mathbf {L}} is given. Using this inequality it is shown that this ordered set can be computed in time O ( n 2 log 2 n ) O(n^2 \log _2 n) , where n = | L | n=|L| .