Assertion: open interval | /r/HasProperty | open set
Facets:
Source sentences:
text: Prove that the closed interval  is a closed set and that the open interval (0,1) is an open set..
text: Open interval: Let a and b be two real numbers such that a<b, then the set of all real numbers lying strictly between a and b is called an open interval and is denoted by ]a, b[ or (a, b).