1941 B. Dushnik & E. W. Miller in 63 600 A system is called a partial order if the following conditions are satisfied. (1) If x < y then y ≮ x; and (2) if x < y and y < z, then x < z.
1990 1 41 A bilattice is a set equipped with two partial orders and a negation operation that inverts one of them while leaving the other unchanged.