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COMBINATORICS
2004
14 years 9 months ago
2004
In this paper we bring together the areas of combinatorics and propositional satisfiability. Many combinatorial theorems establish, often constructively, the existence of positive...
COMBINATORICS
2006
14 years 9 months ago
2006
A homomorphism from an oriented graph G to an oriented graph H is a mapping from the set of vertices of G to the set of vertices of H such that -----(u)(v) is an arc in H whenever...
COMBINATORICS
2006
14 years 9 months ago
2006
A permutation is said to avoid the permutation if no subsequence in has the same order relations as . Two sets of permutations 1 and 2 are Wilfequivalent if, for all n, the numb...
COMBINATORICS
2006
14 years 9 months ago
2006
Simple families of increasing trees can be constructed from simply generated tree families, if one considers for every tree of size n all its increasing labellings, i. e. labellin...
COMBINATORICS
2006
14 years 9 months ago
2006
A differential poset is a partially ordered set with raising and lowering operators U and D which satisfy the commutation relation DU-UD = rI for some constant r. This notion may ...