Formally, the order among cardinal numbers is defined as follows: |X| ≤ |Y| means that there exists an injective function from X to Y. The Cantor–Bernstein–Schroeder theorem states that if |X| ≤ |Y| and |Y| ≤ |X| then |X| = |Y|. The axiom of choice is equivalent to the statement that given two sets X and Y, either |X| ≤ |Y| or |Y| ≤ |X|
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Anonymous2013-08-31 8:43
The infinity symbol \infty (sometimes called the lemniscate) is a mathematical symbol representing the concept of infinity. The symbol is encoded in Unicode at U+221E ∞ infinity (HTML: ∞ ∞) and in LaTeX as \infty.
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Anonymous2013-08-31 9:29
In languages that do not provide explicit access to such values from the initial state of the program, but do implement the floating point data type, the infinity values might still be accessible and usable as the result of certain operations.
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Anonymous2013-08-31 10:15
Combinatorial set theory concerns extensions of finite combinatorics to infinite sets. This includes the study of cardinal arithmetic and the study of extensions of Ramsey's theorem such as the Erdős–Rado theorem.
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Anonymous2013-08-31 11:00
A choice function is a function f, defined on a collection X of nonempty sets, such that for every set s in X, f(s) is an element of s. With this concept, the axiom can be stated: