See also: Ø [U+00D8 LATIN CAPITAL LETTER O WITH STROKE]
, ⌀ [U+2300 DIAMETER SIGN], and ø [U+00F8 LATIN SMALL LETTER O WITH STROKE]
The set-theoretic meaning of this symbol was introduced by the Bourbaki group in their treatise Éléments de mathématique. André Weil has said in his autobiography that he based it on the Norwegian letter Ø.
- (set theory) A set with no elements: the empty set.
- (linguistics) A null form. Ø is commonly used instead.
- See ⌀ for the diameter sign.
- ^ A. Weil, The Apprenticeship of a Mathematician, chapter V "Strasbourg and Bourbaki", p. 114; Birkhäuser Verlag 1992