How to type Empty Set
To type Empty Set (∅), press Alt + 8709 on Windows, holding Alt while typing the digits on the numeric keypad, or press Option + O on Mac, or write ∅ in HTML. On any system you can copy it from this page, or enter its codepoint U+2205 directly: Ctrl+Shift+U then 2205 on Linux, or 2205 then Alt+X in Microsoft Word.
Empty Set
- Copy it
- Unicode
- U+2205
- Windows
- Alt + 8709 needs regedit
| Where | Shortcut | How |
|---|---|---|
| Windows | Alt + 8709 | Above 255, so Windows will not accept it as typed. Copy the character instead. |
| Mac | Option + O | Press the keys together. |
| HTML | ∅ | Paste this into HTML source. |
| Unicode | U+2205 | EMPTY SET |
Symbols related to Empty Set
The Unicode code chart points from ∅ to Ø, and the rest are filed under operator, mathematics and set in CLDR, the keyword list Unicode publishes alongside the names.
Other math symbols
∅ lives in the Mathematical Operators block (U+2200-U+22FF), the core set of mathematical and logical operators. Within Unicode it is classified as Sm, a mathematical symbol. Software may lay it out with the spacing an operator expects.
What Empty Set is used for
In mathematical notation ∅ is an ordinary symbol: it carries no special spacing and sits in an expression the way a letter does, standing for a thing rather than doing something to the things around it. That is the classification unicode-math gives it, and it is what decides how the symbol is set: $\varnothing$ in LaTeX, in maths mode rather than in a sentence.
Unicode publishes a second list of names for ∅ in CLDR, the keywords its own search data offers rather than the formal name, and they are mathematics and operator. Those words are what somebody looking for this character is liable to type when Empty Set is not the name they know it by, and the search on the symbol lists matches them as well as the Unicode name.
What Unicode says about Empty Set
The standard recognises ∅ under another name as well: null set. That is a formal alias, not a nickname, which is why it turns up in other people's documentation for the same codepoint.
Unicode annotates ∅ directly. Against U+2205 the code chart carries the note “Used in linguistics to indicate a null morpheme or phonological "zero"”. That is the standard saying what the character is for, rather than an inference from its name.
The code chart points from ∅ to Capital O with Stroke and diameter sign (U+2300). These are the characters the standard thinks you might have meant instead, which makes them the ones worth checking when Empty Set looks nearly right but not quite.
How Empty Set behaves in software
∅ takes one column in a terminal. It carries no direction of its own, so in a line that mixes English with Arabic or Hebrew it takes the direction of the text around it rather than forcing one.
What people ask about Empty Set
How to type or operator in keyboard?
You can press Alt + 8709 on Windows, with Num Lock on and the digits typed on the numeric keypad, or press Option + O on Mac. Either produces ∅.
Every way to write Empty Set
| Form | Value |
|---|---|
| Codepoint | U+2205 |
| Decimal | 8709 |
| UTF-8 bytes | E2 88 85 |
| UTF-16 bytes | 22 05 |
| HTML entity | ∅ |
| HTML numeric | ∅ or ∅ |
| CSS | \2205 |
| JavaScript | \u2205 |
| Python | \u2205 |
| URL-encoded | %E2%88%85 |
| LaTeX, in maths mode | $\varnothing$ |
| SVG | 2205.svg · (SIL Open Font License) |
If ∅ arrives as ∅
Its three UTF-8 bytes E2 88 85 are being read one at a time as Windows-1252. The text is undamaged; the reader has to be told it is UTF-8.