Definition (First-countable)
is first-countable if, for every , there exists a sequence of neighbourhoods of such that, for any neighbourhood of , there exists with .
Remark
Looking at the definition of Second-countable we can see that this weakens that notion by saying each point has a countable Neighbourhood Basis i.e. the countable collection of neighbourhoods forms a neighbourhood basis in the sense that for any other neighbourhood of we can find an index that points us to something in the basis s.t. .