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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 ...
In the formal language of the Zermelo–Fraenkel axioms, the axiom is expressed as follows: [2] ( ( ()) ( ( (( =))))). In technical language, this formal expression is interpreted as "there exists a set 𝐼 (the set that is postulated to be infinite) such that the empty set is an element of it and, for every element of 𝐼, there exists an element of 𝐼 consisting of just the elements of ...
There is an infinite set of real numbers without a countably infinite subset. The real numbers are a countable union of countable sets. [39] This does not imply that the real numbers are countable: As pointed out above, to show that a countable union of countable sets is itself countable requires the Axiom of countable choice.
For example, one infinity—the one most people are familiar with—is an infinite set of natural numbers: 1, 2, 3, and so on. However, there’s also an infinite set of real numbers, which ...
An infinite set is a set with an infinite number of elements. If the pattern of its elements is obvious, an infinite set can be given in roster notation, with an ellipsis placed at the end of the list, or at both ends, to indicate that the list continues forever. For example, the set of nonnegative integers is
the set of all binary strings of finite length, and; the set of all finite subsets of any given countably infinite set. These infinite ordinals: ω, ω + 1, ω⋅2, ω 2 are among the countably infinite sets. [6] For example, the sequence (with ordinality ω⋅2) of all positive odd integers followed by all positive even integers
An infinite set can simply be defined as one having the same size as at least one of its proper parts; this notion of infinity is called Dedekind infinite. The diagram to the right gives an example: viewing lines as infinite sets of points, the left half of the lower blue line can be mapped in a one-to-one manner (green correspondences) to the ...
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