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Set-builder notation can be used to describe a set that is defined by a predicate, that is, a logical formula that evaluates to true for an element of the set, and false otherwise. [2] In this form, set-builder notation has three parts: a variable, a colon or vertical bar separator, and a predicate. Thus there is a variable on the left of the ...
The last of these notations refers to the union of the collection {:}, where I is an index set and is a set for every . In the case that the index set I is the set of natural numbers , one uses the notation ⋃ i = 1 ∞ A i {\textstyle \bigcup _{i=1}^{\infty }A_{i}} , which is analogous to that of the infinite sums in series.
An important special case is when the index set is , the natural numbers: this Cartesian product is the set of all infinite sequences with the i-th term in its corresponding set X i. For example, each element of ∏ n = 1 ∞ R = R × R × ⋯ {\displaystyle \prod _{n=1}^{\infty }\mathbb {R} =\mathbb {R} \times \mathbb {R} \times \cdots } can ...
This notation is called set-builder notation (or "set comprehension", particularly in the context of Functional programming). Some variants of set builder notation are: {x ∈ A | P(x)} denotes the set of all x that are already members of A such that the condition P holds for x.
The algebra of sets is the set-theoretic analogue of the algebra of numbers. Just as arithmetic addition and multiplication are associative and commutative, so are set union and intersection; just as the arithmetic relation "less than or equal" is reflexive, antisymmetric and transitive, so is the set relation of "subset".
In summary, a set of the real numbers is an interval, if and only if it is an open interval, a closed interval, or a half-open interval. [4] [5] A degenerate interval is any set consisting of a single real number (i.e., an interval of the form [a, a]). [6] Some authors include the empty set in this definition.
Set 3-1 has three possible versions: [0 1 1 1 2 T], [0 1 1 T E 1], and [0 T T 1 E 1], where the subscripts indicate adjacency intervals. The normal form is the smallest "slice of pie" (shaded) or most compact form, in this case: [0 1 1 1 2 T]. This is a list of set classes, by Forte number. [1]
Expressions definable in set-builder notation make sense in both ZFC and NFU: it may be that both theories prove that a given definition succeeds, or that neither do (the expression {} fails to refer to anything in any set theory with classical logic; in class theories like NBG this notation does refer to a class, but it is defined differently ...