olemus
funktsiooni f selliste argumentide x hulk,
mille korral funktsiooni f väärtus f(x) on määratud,
st leidub y, mille puhul
järjestatud paar (x,y) on funktsiooni f kui binaarseose element

Wiktionary:
4. (mathematics) the set of all possible mathematical entities (points) where a given function is defined
5. (mathematics, set theory) the set of input (argument) values for which a function is defined

ülevaateid
https://www.mathsisfun.com/definitions/domain-of-a-function.html

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

https://www.mathsisfun.com/sets/domain-range-codomain.html

https://math.libretexts.org/Bookshelves/Algebra/Map%3A_College_Algebra_(OpenStax)/03%3A_Functions/3.03%3A_Domain_and_Range

näiteid
https://mathbitsnotebook.com/Algebra1/Functions/FNDomainRange.html

https://www.mathwords.com/d/domain.htm

https://cnx.org/contents/4s00i8Fu@7/Domain-and-range-of-exponential-and-logarithmic-function