Editing Empty set (section)

==Notation==
{{Main|Null sign}}
[[Image:Empty set symbol.svg|thumb|upright=0.6|A symbol for the empty set]]
Common notations for the empty set include "{ }", "<math>\emptyset</math>", and "∅". The latter two symbols were introduced by the [[Bourbaki group]] (specifically [[André Weil]]) in 1939, inspired by the letter [[Ø]] ({{unichar|d8|LATIN CAPITAL LETTER O WITH STROKE}}) in the [[Danish orthography|Danish]] and [[Norwegian orthography|Norwegian]] alphabets.<ref>{{cite web| url = http://jeff560.tripod.com/set.html| title = Earliest Uses of Symbols of Set Theory and Logic.}}</ref> In the past, "0" (the numeral [[zero]]) was occasionally used as a symbol for the empty set, but this is now considered to be an improper use of notation.<ref>{{Cite book|url=https://archive.org/details/1979RudinW|title=Principles of Mathematical Analysis|last=Rudin|first=Walter|publisher=McGraw-Hill|year=1976|isbn=007054235X|edition=3rd|pages=300}}</ref>

The symbol ∅ is available at [[Unicode]] point {{unichar|2205|EMPTY SET}}.<ref>{{cite web| url = https://www.unicode.org/charts/PDF/U2200.pdf| title = Unicode Standard 5.2}}</ref> It can be coded in [[HTML]] as {{code|&empty;}} and as {{code|&#8709;}} or as {{code|&#x2205;}}. It can be coded in [[LaTeX]] as {{code|\varnothing}}. The symbol <math>\emptyset</math> is coded in LaTeX as {{code|\emptyset}}.

When writing in languages such as Danish and Norwegian, where the empty set character may be confused with the alphabetic letter Ø (as when using the symbol in linguistics), the Unicode character U+29B0 REVERSED EMPTY SET ⦰ may be used instead.<ref>e.g. Nina Grønnum (2005, 2013) ''Fonetik og Fonologi: Almen og dansk.'' Akademisk forlag, Copenhagen.</ref>