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A totally ordered set is a partially ordered set in which any two elements are comparable. The Szpilrajn extension theorem states that every partial order is contained in a total order. Intuitively, the theorem says that any method of comparing elements that leaves some pairs incomparable can be extended in such a way that every pair becomes ...
Next it is shown that the poset of partial orders extending , ordered by extension, has a maximal element. The existence of such a maximal element is proved by applying Zorn's lemma to this poset. Zorn's lemma states that a partial order in which every chain has an upper bound has a maximal element. A chain in this poset is a set of relations ...
A partially ordered set (poset for short) is an ordered pair = (,) consisting of a set (called the ground set of ) and a partial order on . When the meaning is clear from context and there is no ambiguity about the partial order, the set X {\displaystyle X} itself is sometimes called a poset.
In the particular case of a partially ordered set, while there can be at most one maximum and at most one minimum there may be multiple maximal or minimal elements. [ 1 ] [ 2 ] Specializing further to totally ordered sets , the notions of maximal element and maximum coincide, and the notions of minimal element and minimum coincide.
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.
A figure of speech or rhetorical figure is a word or phrase that intentionally deviates from straightforward language use or literal meaning to produce a rhetorical or intensified effect (emotionally, aesthetically, intellectually, etc.). [1] [2] In the distinction between literal and figurative language, figures of
One of the most important differences between a greatest element and a maximal element of a preordered set (,) has to do with what elements they are comparable to. Two elements x , y ∈ P {\displaystyle x,y\in P} are said to be comparable if x ≤ y {\displaystyle x\leq y} or y ≤ x {\displaystyle y\leq x} ; they are called incomparable if ...
An antichain in a partially ordered set is a set of elements no two of which are comparable to each other, and a chain is a set of elements every two of which are comparable. A chain decomposition is a partition of the elements of the order into disjoint chains. Dilworth's theorem states that, in any finite partially ordered set, the largest ...