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Any set which can be mapped onto an infinite set is infinite. The Cartesian product of an infinite set and a nonempty set is infinite. The Cartesian product of an infinite number of sets, each containing at least two elements, is either empty or infinite; if the axiom of choice holds, then it is infinite. If an infinite set is a well-ordered ...
A set of polygons in an Euler diagram This set equals the one depicted above since both have the very same elements.. In mathematics, a set is a collection of different [1] things; [2] [3] [4] these things are called elements or members of the set and are typically mathematical objects of any kind: numbers, symbols, points in space, lines, other geometrical shapes, variables, or even other ...
For a ≤ b, the closed interval [a, b] is the set of elements x satisfying a ≤ x ≤ b (that is, a ≤ x and x ≤ b). It contains at least the elements a and b. Using the corresponding strict relation "<", the open interval (a, b) is the set of elements x satisfying a < x < b (i.e. a < x and x < b). An open interval may be empty even if a < b.
The supremum (abbreviated sup; pl.: suprema) of a subset of a partially ordered set is the least element in that is greater than or equal to each element of , if such an element exists. [1] If the supremum of S {\displaystyle S} exists, it is unique, and if b is an upper bound of S {\displaystyle S} , then the supremum of S {\displaystyle S} is ...
As an example of an application of AC ω, here is a proof (from ZF + AC ω) that every infinite set is Dedekind-infinite: [2] Let X {\displaystyle X} be infinite. For each natural number n {\displaystyle n} , let A n {\displaystyle A_{n}} be the set of all n {\displaystyle n} -tuples of distinct elements of X {\displaystyle X} .
Infinite groups can also have finite generating sets. The additive group of integers has 1 as a generating set. The element 2 is not a generating set, as the odd numbers will be missing. The two-element subset {3, 5} is a generating set, since (−5) + 3 + 3 = 1 (in fact, any pair of coprime numbers is, as a consequence of Bézout's identity).
Here the underlying set of elements is the set of prime factors of n. For example, the number 120 has the prime factorization =, which gives the multiset {2, 2, 2, 3, 5}. A related example is the multiset of solutions of an algebraic equation. A quadratic equation, for example, has two solutions. However, in some cases they are both the same ...
Using first-order logic primitive symbols, the axiom can be expressed as follows: [2] ( ( ()) ( ( (( =))))). In English, this sentence means: "there exists a set 𝐈 such that the empty set is an element of it, and for every element of 𝐈, there exists an element of 𝐈 such that is an element of , the elements of are also elements of , and nothing else is an element of ."