Weighted spanning trees on some self-similar graphs.
Well-rounded sublattices of planar lattices
A lattice in Euclidean d-space is called well-rounded if it contains d linearly independent vectors of minimal length. This class of lattices is important for various questions, including sphere packing or homology computations. The task of enumerating well-rounded sublattices of a given lattice is of interest already in dimension 2, and has recently been treated by several authors. In this paper, we analyse the question more closely in the spirit of earlier work on similar sublattices and coincidence...
Wilf classes of pairs of permutations of length 4.
William Chen grammars and derivations in trees and arborescences. (Grammaires de William Chen et dérivations dans les arbres et arborescences.)
Words avoiding a reflexive acyclic relation.
Words restricted by patterns with at most 2 distinct letters.