Venn diagrams and symmetric chain decompositions in the Boolean lattice.
Visibility Graphs of Staircase Polygons and the Weak Bruhat Order, I: from Visibility Graphs to Maximal Chains.
Where the typical set partitions meet and join.
Words avoiding a reflexive acyclic relation.
Wreath products of permutation classes.
σ-Entangled linear orders and narrowness of products of Boolean algebras
We investigate σ-entangled linear orders and narrowness of Boolean algebras. We show existence of σ-entangled linear orders in many cardinals, and we build Boolean algebras with neither large chains nor large pies. We study the behavior of these notions in ultraproducts.