Practice problem
Let XXX be a topological space and Y={ξ}Y = \{\xi\}Y={ξ} a singleton subspace of XXX. (Here ξ\xiξ is just a point of XXX.) When does a point p∈Xp\in Xp∈X lie in the closure Y‾\overline{Y}Y?
If and only if ξ\xiξ lies in the intersection of all open neighborhoods UUU of ppp.
If and only if ξ\xiξ lies in the intersection of all closed sets CCC containing ppp.
None of the above.
Type a concept, like “slope” or “photosynthesis”.