olemus
elementideta hulk
=
a set without any elements

ülevaateid
https://en.wikipedia.org/wiki/Empty_set

https://mathworld.wolfram.com/EmptySet.html

https://blogs.scientificamerican.com/roots-of-unity/a-few-of-my-favorite-spaces-the-empty-set/

https://www.cuemath.com/algebra/empty-set/