What ⨟ means
It combines two Z schemas, or named system descriptions. A schema is a named block of variables and conditions describing a system state or operation. Variables for the state after the first operation match those for the state before the second; Z hides that shared intermediate state in the result.
Z was conceived in the late 1970s to describe computing systems with mathematics and developed through the 1980s. Its first widely published reference manual appeared in 1989. Z draws on set theory, the mathematics of collections, and predicate logic, which expresses conditions that can be true or false.
Use ⨟ only in Z notation
It is an operator in Z’s schema calculus, the rules for combining schemas. It does not stand for general function or relation composition.
Don't confuse it with
1Questions 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 ⨟
⨟\2A1FCodes and encoding1 code points
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.