What ⟺ means
It joins statements that imply each other.
A⟺B means that A is true exactly when B is true.
The shorter equivalence arrow is documented by 1936; a double-line form by 1954. Those dates trace the notation family, not this exact long glyph.
When is it more than iff?
Between constructions, it can mark correspondence.
That reading is looser than a proved biconditional; context must establish whether both directions hold.
Formal mathematical notation used in logic and proofs.
A loose correspondence does not prove both directions.
Don't confuse it with
1Questions people ask
1Why does ⟺ look different across documents?
Font choice changes its width, spacing, and stroke weight.
How to type ⟺
Windows (Word)
Alt+XType 27FA, then Alt+X to get ⟺.
Windows
Win+Rrun charmap for the full table, or use the emoji picker's Ω symbols tab (Win + .).
macOS
Control+Command+SpaceOpen the character viewer and search “long left right double arrow”.
Linux
Ctrl+Shift+UType 27fa, then Enter or Space.
HTML
⟺CSS
\27FALaTeX
Use \Longleftrightarrow in math mode.
Codes and encoding1 code points
HTML decimal
⟺
HTML hex
⟺
CSS content
content: "\27FA";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%9F%BA
1
On screen
1
Code points
1
JS .length
3
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.