Relation domain
Set
context | $ R $ |
$ c\in R $ | |
postulate | $ \forall c.\ \exists a,b.\ c=\langle a,b\rangle $ |
definiendum | $ x\in \mathrm{dom}(R) $ |
postulate | $ \exists y.\ \langle x,y \rangle\in R $ |
Discussion
Reference
Wikipedia: Domain of a function