XYZ inequality
INEQUALITY FOR THE NUMBER OF EXTENSIONS OF PARTIAL ORDERS TO LINEAR ORDERS
XYZ conjecture; Fishburn-Shepp inequality; Fishburn–Shepp inequality
In combinatorial mathematics, the XYZ inequality, also called the Fishburn–Shepp inequality, is an inequality for the number of linear extensions of finite partial orders. The inequality was conjectured by Ivan Rival and Bill Sands in 1981.