In mathematics, an interval usually refers to a set of real numbers: if X and Y are two numbers in a set, then any number between X and Y also belongs to the set.
For example, a set consisting of real numbers that conform to 0≤x≤ 1 is an interval, which includes 0, 1 and all real numbers between 0 and 1. Other examples are: real number set, negative real number set, etc.
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