| Definition: | set of real numbers such that, for any pair (x, y) of elements of the set, any real number z between x and y belongs to the set NOTE There are several kinds of intervals: - closed interval from a to b: [a, b]={x∈R | a≤x≤b}
- open interval from a to b: ]a, b[={x∈R | a<x<b}
- half-open intervals: ]a, b]={x∈R | a<x≤b} and [a, b[={x∈R | a≤x<b}
- closed unbounded interval up to b or onward from a: ]−∞, b]={x∈R | x≤b} and [a, +∞[={x∈R | a≤x}
- open unbounded interval up to b or onward from a: ]−∞, b[={x∈R | x<b} and ]a, +∞[={x∈R | a<x}
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