What ⊐ means
It denotes a square-superset relation in mathematical notation.
Unicode calls it “square original of”; mathematical references also call it “square superset.” The square form distinguishes it from curved ⊃, and the source’s definitions establish the exact relation.
Technical and specialist; check the surrounding notation for its exact meaning.
Don’t replace a source’s ⊃ with ⊐; the square form may mark a different relation.
Don't confuse it with
1Questions people ask
1Is ⊐ the same as ⊃?
No. ⊐ is the square form; ⊃ is the ordinary curved superset relation. Whether that distinction changes the rule depends on the text’s notation.
How to type ⊐
Windows (Word)
Alt+XType 2290, 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 “square original of”.
Linux
Ctrl+Shift+UType 2290, then Enter or Space.
HTML
⊐CSS
\2290How do I type ⊐ in LaTeX?
Use `\sqsupset`; in LaTeX, load `amssymb`. Plain TeX does not provide the command.
Codes and encoding1 code points
HTML decimal
⊐
HTML hex
⊐
CSS content
content: "\2290";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%8A%90
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.