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The endpoint adjoining the square bracket is known as closed, while the endpoint adjoining the parenthesis is known as open. If both types of brackets are the same, the entire interval may be referred to as closed or open as appropriate. Whenever infinity or negative infinity is used as an endpoint (in the case of intervals on the real number ...
An interval is said to be left-open if and only if it contains no minimum (an element that is smaller than all other elements); right-open if it contains no maximum; and open if it contains neither. The interval [0, 1) = {x | 0 ≤ x < 1}, for example, is left-closed and right-open. The empty set and the set of all reals are both open and ...
[45] [46] The endpoint adjoining the square bracket is known as closed, whereas the endpoint adjoining the parenthesis is known as open. [44] In group theory and ring theory, brackets denote the commutator. In group theory, the commutator [g, h] is commonly defined as g −1 h −1 g h .
Beyond elementary mathematics, [] are mostly used for other purposes, e.g. to denote a closed interval, or an equivalence class, so they appear rarely for grouping. The usage of the word "brackets" varies from country. In the United States, the term denotes [], known elsewhere as "square brackets".
Order of operations, uses multiple types of brackets; Set, uses braces "{}" Interval, uses square brackets and parentheses; Matrix, uses square brackets and parentheses; Inner product space, uses parentheses and chevrons
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Conversely, if closed sets are given and every intersection of closed sets is closed, then one can define a closure operator C such that () is the intersection of the closed sets containing X. This equivalence remains true for partially ordered sets with the greatest-lower-bound property , if one replace "closed sets" by "closed elements" and ...