Null sign

The symbol ∅ is available at Unicode point U+2205.[https://www.unicode.org/charts/PDF/U2200.pdf Unicode Standard 5.2] It can be coded in HTML as {{mono|∅}} and as {{mono|∅}} or as {{mono|∅}}. It can be coded in LaTeX as {{mono|\varnothing}}.

Similar letters and symbols include the following:

• Diameter sign in geometry: {{unichar|2300|Diameter Sign}}
• Scandinavian letter Ø: majuscule {{unichar|00D8|Latin Capital Letter O with Stroke}} and minuscule {{unichar|00F8|Latin Small Letter O with Stroke}} are a part of the alphabet of Scandinavian languages. The minuscule letter is also used in the International Phonetic Alphabet (IPA) to represent close-mid front rounded vowel.
• Greek letter Φ: majuscule {{unichar|03A6|Greek Capital Letter Phi}} and minuscule {{unichar|03C6|Greek Small Letter Phi}} are a part of the Greek alphabet. It sometimes take the form of {{unichar|03D5|Greek Phi Symbol}} and is used as a sign in different fields of studies. The {{unichar|0278|Latin Small Letter Phi}} is used in the IPA for voiceless bilabial fricative.
• Greek letter Θ: majuscule {{unichar|0398|Greek Capital Letter Theta}} and minuscule {{unichar|03B8|Greek Small Letter Theta}} are a part of the Greek alphabet. The minuscule is used in the IPA for voiceless dental fricative. The capital letter sometimes are rendered as {{unichar|03F4|Greek Capital Theta Symbol}}.
• Cyrillic letter Ө: majuscule {{unichar|04E8|Cyrillic Capital Letter Barred O}} and minuscule {{unichar|04E9|Cyrillic Small Letter Barred O}} are a part of the Cyrillic script. It is used in the IPA for close-mid central rounded vowel.
• Cyrillic letter Ф: majuscule {{unichar|0424|Cyrillic Capital Letter Ef}} and minuscule {{unichar|0444|Cyrillic Small Letter Ef}} are a part of the Cyrillic script. The letter took the place of fita ({{unichar|0472|Cyrillic Capital Letter Fita}} and {{unichar|0473|Cyrillic Small Letter Fita}}), a letter of Early Cyrillic alphabet in modern usages.

In mathematics, the null sign (∅) denotes the empty set.{{cite web |last1=Lankham |first1=Isaiah |last2=Nachtergaele |first2=Bruno |last3=Schilling |first3=Anne |title=Some Common Mathematical Symbols and Abbreviations (with History) |url=https://www.math.ucdavis.edu/~anne/WQ2007/mat67-Common_Math_Symbols.pdf |website=University of California, Davis |access-date=2 May 2025 |page=2 |date=January 21, 2007}}{{cite book |last1=Gerstein |first1=Larry J. |title=Introduction to Mathematical Structures and Proofs |date=2012 |publisher=Springer |location=New York |isbn=9781461442653 |pages=42-43 |url=https://www.google.com.au/books/edition/Introduction_to_Mathematical_Structures/qK9y768b1NQC?hl=en&gbpv=0 |access-date=2 May 2025}} Note that a null set is not necessarily an empty set. Common notations for the empty set include "{}", "∅", and "$\backslash emptyset$". The latter two symbols were introduced by the Bourbaki group (specifically André Weil) in 1939, inspired by the letter Ø in the Danish and Norwegian alphabets (and not related in any way to the Greek letter Φ).{{cite web|url=http://jeff560.tripod.com/set.html|title=Earliest Uses of Symbols of Set Theory and Logic|website=jeff560.tripod.com}}

Empty sets are used in set operations. For example:

$A=\backslash \{2,3,5,7,11\backslash \}$

$B=\backslash \{4,6,8,9\backslash \}$

$A\; \backslash cap\; B\; =\; ?$

There are no common elements in the solution; so it should be denoted as:

$A\; \backslash cap\; B\; =\; \backslash varnothing$ or $A\; \backslash cap\; B\; =\; \backslash \{\; \backslash \}$

{{See also|Zero (linguistics)|Silent letter|Null morpheme}}

In linguistics, the null sign is used to indicate the absence of an element, such as a phoneme or morpheme.{{cite book |last1=Pullum |first1=Geoffrey K. |last2=Ladusaw |first2=William A. |title=Phonetic Symbol Guide |date=2013 |publisher=University of Chicago Press |isbn=9780226924885 |pages=136-137 |url=https://www.google.com.au/books/edition/Phonetic_Symbol_Guide/b7ml0qh2HMcC?hl=en&gbpv=1 |access-date=2 May 2025}}

The English language was a fusional language, this means the language makes use of inflectional changes to convey multiple grammatical meanings. Although the inflectional complexity of English has been largely reduced in the course of development, the inflectional endings can be seen in earlier forms of English, such as Early Modern English (abbreviated as EModE).

The verb endings of EModE were summarised in the table below by Roger Lass:Lass, R. (1999). Phonology and Morphology. In R. Lass (Ed.), The Cambridge History of the English Language: 1476-1776 (Vol. 3, pp. 137-180). Cambridge, UK: Cambridge University Press.

In photography the null sign, Ø, found on camera lenses denotes the filter thread diameter, measured in millimeters. This marking indicates the size of screw-in filters that can be attached to the front of the lens. This diameter is separate from any optical specification of the lens, as it is a standardized measurement for photographers to select a compatible filter. Common filter thread sizes include 52mm, 72mm, 77mm, and 82mm. If a photographer owns multiple lenses with different filter thread diameters, stepping rings can be utilized to adapt larger filters to smaller lens threads, eliminating the need to purchase duplicate filters in various sizes.

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Category:Mathematical symbols