[a;b[ I want to do a problem with this but i can't find anything about it, if anyone can help me it'd be very useful, thank you. :) The one i want to do exactly is [20;30[ , in case anyone is wondering.
Google says... http://en.wikipedia.org/wiki/ISO_31-11#Sets The endpoint of an open interval can be expressed with an outward-facing square bracket which is synonymous with an inward-facing parenthesis.
In other words, [20;30[ means {x | 20 ≤ x < 30}, the interval on the real number line between 20 and 30, with 20 included and 30 excluded.
Perhaps you are familiar with [20, 30), another notation meaning the same thing- all numbers between 20 and 30, including 20 but not 30.