On the system of all maximal chains (antichains) of a graph.
On the theory of Pfaffian orientations. I: Perfect matchings and permanents.
On the theory of Pfaffian orientations. II: -joins, -cuts, and duality of enumeration.
On the volume of a certain polytope.
On the volume of the polytope of doubly stochastic matrices.
On two combinatorial identities
On Zeilberger's constant term for Andrew's TSSCPP theorem.
On-line Ramsey theory.
Operatorenkalkül über freien Monoiden I: Strukturen.
Operatorenkalkül über freien Monoiden II: Binominalsysteme.
Operatorenkalkül über freien Monoiden III: Lagrangeinversion und Sheffersysteme.
Optimal Penney Ante strategy via correlation polynomial identities.
Orders with ten elements are circle order.
Osculating paths and oscillating tableaux.
-adic analysis and classical sequences of numbers. (Analyse -adique et suites classiques de nombres.)
Packing densities of patterns.
Packing patterns into words.
Parametric production matrices and weighted succession rules: a Dyck path example.
Parity theorems for statistics on domino arrangements.
Parity theorems for statistics on permutations and Catalan words.