<sod>Infinity is not a number, because doing arithmetic with infinity leads to contradictions, but infinity can be added to the standard number systems in various ways.  In calculus, [[limit (mathematics)| limits]] often involve infinity, and in [[set theory]] includes infinite sets. <eod>
<sod>Infinity is not a number, because doing arithmetic with infinity leads to contradictions, but infinity can be added to the standard number systems in various ways.  In calculus, [[limit (mathematics)| limits]] often involve infinity, and [[set theory]] includes infinite sets. <eod>