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The maximum of a subset of a preordered set is an element of which is greater than or equal to any other element of , and the minimum of is again defined dually. 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.
Symmetric difference = {: ()} is sometimes associated with exclusive or (xor) (also sometimes denoted by ), in which case if the order of precedence from highest to lowest is ,,, then the order of precedence (from highest to lowest) for the set operators would be , ,,.
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 ...
The relationship between sets established by ⊆ is called inclusion or containment. Equality between sets can be expressed in terms of subsets. Two sets are equal if and only if they contain each other: that is, A ⊆ B and B ⊆ A is equivalent to A = B. [30] [8] The empty set is a subset of every set: ∅ ⊆ A. [17] Examples:
A subset is cofinal in the whole set if and only if it is unbounded in the whole set or it has a maximum that is also maximum of the whole set. A well-ordered set as topological space is a first-countable space if and only if it has order type less than or equal to ω 1 ( omega-one ), that is, if and only if the set is countable or has the ...
The concepts of infimum and supremum are close to minimum and maximum, but are more useful in analysis because they better characterize special sets which may have no minimum or maximum. For instance, the set of positive real numbers + (not including ) does not have a minimum, because any given element of + could simply be divided in half ...
In mathematics, the limit of a sequence of sets,, … (subsets of a common set ) is a set whose elements are determined by the sequence in either of two equivalent ways: (1) by upper and lower bounds on the sequence that converge monotonically to the same set (analogous to convergence of real-valued sequences) and (2) by convergence of a sequence of indicator functions which are themselves ...
A set with a partial order on it is called a partially ordered set, poset, or just ordered set if the intended meaning is clear. By checking these properties, one immediately sees that the well-known orders on natural numbers , integers , rational numbers and reals are all orders in the above sense.