Editing Partition of an interval (section)

==Refinement of a partition==
Another partition {{mvar|Q}} of the given interval [a, b] is defined as a '''refinement of the partition''' {{mvar|P}}, if {{mvar|Q}} contains all the points of {{mvar|P}} and possibly some other points as well; the partition {{mvar|Q}} is said to be “finer” than {{mvar|P}}. Given two partitions, {{mvar|P}} and {{mvar|Q}}, one can always form their '''common refinement''', denoted {{math|''P''&nbsp;∨&nbsp;''Q''}}, which consists of all the points of {{mvar|P}} and {{mvar|Q}}, in increasing order.<ref>{{cite book|last=Brannan|first=D. A.|title=A First Course in Mathematical Analysis|publisher=Cambridge University Press|year=2006|isbn=9781139458955|page=262|url=https://books.google.com/books?id=N8bL9lQUGJgC&pg=PA262}}</ref>