Definition:Real Interval/Notation/Reverse-Bracket

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In order to avoid the ambiguity problem arising from the conventional notation for intervals where an open real interval can be confused with an ordered pair, some authors use the reverse-bracket notation for open and half-open intervals:

\(\ds \left ] {\, a, b} \right [\) \(:=\) \(\ds \set {x \in \R: a < x < b}\) Open real interval
\(\ds \left [ {a, b} \right [\) \(:=\) \(\ds \set {x \in \R: a \le x < b}\) Half-open on the right
\(\ds \left ] {\, a, b} \right ]\) \(:=\) \(\ds \set {x \in \R: a < x \le b}\) Half-open on the left

These are often considered to be both ugly and confusing, and hence are limited in popularity.