What ⇍ means
It negates the leftwards double arrow ⇐.
In logic, A ⇍ B denies the leftward implication A ⇐ B: A does not follow from B. Other notation may assign ⇐ a different relation, so read the surrounding formula.
Bourbaki's 1954 work documents the broader double-arrow convention; that date does not establish when ⇍ first appeared.
Don't confuse it with
3⇐⇎↚
Leftwards Double Arrow
The unbarred form lacks the crossing stroke; if ⇍ renders faintly, the two can be hard to distinguish.
Left Right Double Arrow With Stroke
It negates the left-right double arrow, not only a leftward one.
Leftwards Arrow With Stroke
It negates a single leftwards arrow with one shaft.
Questions people ask
1Why does ⇍ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ⇍
Windows (Word)
Alt+XType 21CD, 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 “leftwards double arrow with stroke”.
Linux
Ctrl+Shift+UType 21cd, then Enter or Space.
HTML
⇍CSS
\21CDLaTeX
Use `\nLeftarrow` in math mode.
Unicode escape
Use `\u21CD` where Unicode escapes are supported.
HTML
Use `⇍` or `⇍` in HTML.
Codes and encoding1 code points
HTML decimal
⇍
HTML hex
⇍
CSS content
content: "\21CD";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%87%8D
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.