olemus
sõltub kontekstist

näiteid
https://paulrumyancev.medium.com/uml-class-diagram-arrows-guide-37e4b1bb11e

https://en.wikipedia.org/wiki/Function_(mathematics)#Arrow_notation

https://en.wikipedia.org/wiki/Knuth%27s_up-arrow_notation

https://en.wikipedia.org/wiki/Conway_chained_arrow_notation