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denote the poset formed by removing x from P. A poset game on P, played between two players conventionally named Alice and Bob, is as follows: Alice chooses a point x ∈ P; thus replacing P with P x, and then passes the turn to Bob who plays on P x, and passes the turn to Alice. A player loses if it is their turn and there are no points to choose.
In this poset, 60 is an upper bound (though not a least upper bound) of the subset {,,,}, which does not have any lower bound (since 1 is not in the poset); on the other hand 2 is a lower bound of the subset of powers of 2, which does not have any upper bound. If the number 0 is included, this will be the greatest element, since this is a ...
The greatest element of a poset P can be called unit or just 1 (if it exists). Another common term for this element is top. It is the infimum of the empty set and the supremum of P. The dual notion is called zero. Up-set. See upper set. Upper bound. An upper bound of a subset X of a poset P is an element b of P, such that x ≤ b, for all x in X.
2. An inductive definition is a definition that specifies how to construct members of a set based on members already known to be in the set, often used for defining recursively defined sequences, functions, and structures. 3. A poset is called inductive if every non-empty ordered subset has an upper bound infinity axiom See Axiom of infinity.
Thus, an equivalent definition of the dimension of a poset P is "the least cardinality of a realizer of P." It can be shown that any nonempty family R of linear extensions is a realizer of a finite partially ordered set P if and only if, for every critical pair ( x , y ) of P , y < i x for some order < i in R .
Sometimes a graded poset is called a ranked poset but that phrase has other meanings; see Ranked poset. A rank or rank level of a graded poset is the subset of all the elements of the poset that have a given rank value. [1] [2] Graded posets play an important role in combinatorics and can be visualized by means of a Hasse diagram.
A k-Sperner poset is a graded poset in which no union of k antichains is larger than the union of the k largest rank levels, [1] or, equivalently, the poset has a maximum k-family consisting of k rank levels. [2] A strict Sperner poset is a graded poset in which all maximum antichains are rank levels. [2]
Let us use the term “deductive system” as a set of sentences closed under consequence (for defining notion of consequence, let us use e.g. Alfred Tarski's algebraic approach [3] [4]). There are interesting theorems that concern a set of deductive systems being a directed-complete partial ordering. [ 5 ]