U+21D4
| Application | How to insert Left Right Double Arrow |
|---|---|
| Microsoft Word | Type 21D4, then press Alt+X |
| Excel / Google Sheets | Use the formula =UNICHAR(8660) |
| Google Docs | Insert → Special characters, then search "left right double arrow" |
| HTML | ⇔ or ⇔ |
| CSS (content property) | content: "\21D4" |
| JavaScript | "\u21D4" |
The left-right double arrow represents logical equivalence: 'if and only if'.
Used in logic for biconditional statements (P ⇔ Q means 'P if and only if Q'). Also called 'iff' in mathematics.