Empty set
Notation

Common notations for the empty set include "{ }", " ∅ {\displaystyle \emptyset } ", and " ∅ ". The latter two symbols were introduced by the Bourbaki group (specifically André Weil) in 1939, inspired by the letter Ø (U+00D8 Ø LATIN CAPITAL LETTER O WITH STROKE) in the Danish and Norwegian alphabets. 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.

The symbol ∅ is available at Unicode point U+2205 ∅ EMPTY SET. It can be coded in HTML as &empty; and as &#8709; or as &#x2205;. It can be coded in LaTeX as \varnothing. The symbol ∅ {\displaystyle \emptyset } is coded in LaTeX as \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.
punctuation:no_comma, detectable_content:postscript, language:response_language[Spanish]