Applying the Cz\'edli-Schmidt sequences to congruence properties of planar semimodular lattices
G. Gr¤tzer · Discussiones Mathematicae - General Algebra and Applications · 2021
Following Grätzer and Knapp, 2009, a planar semimodular lattice L is rectangular, if the left boundary chain has exactly one doubly-irreducible element, cl, and the right boundary chain has exactly one doubly-irreducible element, cr, and these elements are complementary.