The common useage in mathematics is in analysis and topology, to specify subsets of the real numbers. Remembering that open and closed are jargon terms in topol

The common useage in mathematics is in analysis and topology, to specify subsets of the real numbers. Remembering that open and closed are jargon terms in topology: (a,b) is an open set and contains exactly those x such that a is less than x and x is less than b. [a,b] is a closed set and contains exactly those x such that a is less than or equal to x and x is less than or equal to b For example, one might be thinking about the interval [0,pi] but the function 1/sin x has singularities at both ends of the interval. It is only defined on (0,pi). Notice that 1/x is defined on (0,pi]. It is sometimes convenient to mix up open=exclusive=() and closed=inclusive=[]. These conventions can be carried over into computer science in the obvious way [0,3) = {0,1,2} while (0,3] = {1,2,3} but the motivation is different. In computer science we are more concerned how smoothly our subranges chain together. For example [0,r)+[r,s)+[s,t) = [0,t) while [0,r]+[r+1,s]+[s+1,t] = [0,t]