Topological space
Set A with a family A of its subsets is called topological space, if
the following conditions are satisfied:
- ∅∈A, A∈A
- ∀X1,X2∈A:X1∩X2∈A
- ∀{Xα}⊂A:⋃αXα∈A
Set A with a family A of its subsets is called topological space, if
the following conditions are satisfied: