U+2218 Ring Operator
U+2218 was added in Unicode version 1.1 in 1993. It belongs to the block
This character is a Math Symbol and is commonly used, that is, in no specific script. The character is also known as composite function and APL jot.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. The word that U+2218 forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with one other glyph.
The CLDR project calls this character “ring operator” for use in screen reading software. It assigns these additional labels, e.g. for search in emoji pickers: composition, operator.
The Wikipedia has the following information about this codepoint:
In mathematics, function composition is an operation ∘ that takes two functions f and g, and produces a function h = g ∘ f such that h(x) = g(f(x)). In this operation, the function g is applied to the result of applying the function f to x. That is, the functions f : X → Y and g : Y → Z are composed to yield a function that maps x in domain X to g(f(x)) in codomain Z. Intuitively, if z is a function of y, and y is a function of x, then z is a function of x. The resulting composite function is denoted g ∘ f : X → Z, defined by (g ∘ f )(x) = g(f(x)) for all x in X.
The notation g ∘ f is read as "g of f ", "g after f ", "g circle f ", "g round f ", "g about f ", "g composed with f ", "g following f ", "f then g", or "g on f ", or "the composition of g and f ". Intuitively, composing functions is a chaining process in which the output of function f feeds the input of function g.
The composition of functions is a special case of the composition of relations, sometimes also denoted by $\circ $. As a result, all properties of composition of relations are true of composition of functions, such as the property of associativity.
Composition of functions is different from multiplication of functions (if defined at all), and has some quite different properties; in particular, composition of functions is not commutative.
Representations
System  Representation 

Nº  8728 
UTF8  E2 88 98 
UTF16  22 18 
UTF32  00 00 22 18 
URLQuoted  %E2%88%98 
HTML hex reference  ∘ 
Wrong windows1252 Mojibake  âˆ˜ 
HTML named entity  ∘ 
HTML named entity  ∘ 
alias  composite function 
alias  APL jot 
L^{A}T_{E}X  \circ 
digraph  Ob 
Related Characters
Confusables
Elsewhere
Complete Record
Property  Value 

1.1 (1993)  
RING OPERATOR  
—  
Mathematical Operators  
Math Symbol  
Common  
Other Neutral  
Not Reordered  
none  


✘  




✘  










✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  


Any  
✔  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
0  
0  
0  
✘  
None  
—  
NA  
Other  
—  
✘  
✘  
✔  
✘  
Yes  
Yes  


Yes  


Yes  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✘  
✔  
✘  
✘  
✘  
✘  
Other  
✘  
✘  
✘  
✘  
✘  
Other  
✘  
✘  
✘  
✘  
✘  
✘  
✘  


None  
neutral  
Not Applicable  
—  
No_Joining_Group  
Non Joining  
Alphabetic  
none  
not a number  


R 