What ⨿ means
It combines inputs through one rule about maps. Given maps from both inputs to a destination, there is exactly one matching map from the combined result.
Other settings give direct sums. Gabriel and Zisman used the term “amalgamated sum” in a work from 1967.
Don't confuse it with
1Questions people ask
1Is ⨿ the same as ordinary union?
No. For sets, a coproduct is a disjoint union that tracks which input each element came from; ordinary union merges shared elements.
How to type ⨿
Windows (Word)
Alt+XType 2A3F, 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 “amalgamation or coproduct”.
Linux
Ctrl+Shift+UType 2a3f, then Enter or Space.
HTML
⨿CSS
\2A3FLaTeX
In math mode, use \amalg to typeset ⨿.
Codes and encoding1 code points
HTML decimal
⨿
HTML hex
⨿
CSS content
content: "\2A3F";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%A8%BF
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.