let Y be non empty TopSpace; :: thesis: for x being Point of Y holds MaxADSet x c= meet { F where F is Subset of Y : ( F is closed & x in F ) }
let x be Point of Y; :: thesis: MaxADSet x c= meet { F where F is Subset of Y : ( F is closed & x in F ) }
set G = { F where F is Subset of Y : ( F is closed & x in F ) } ;
[#] Y in { F where F is Subset of Y : ( F is closed & x in F ) } ;
then A1: { F where F is Subset of Y : ( F is closed & x in F ) } <> {} ;
{ F where F is Subset of Y : ( F is closed & x in F ) } c= bool the carrier of Y

proof

let C be object ; :: according to TARSKI:def 3 :: thesis: ( not C in { F where F is Subset of Y : ( F is closed & x in F ) } or C in bool the carrier of Y )
assume C in { F where F is Subset of Y : ( F is closed & x in F ) } ; :: thesis: C in bool the carrier of Y
then ex P being Subset of Y st
( C = P & P is closed & x in P ) ;
hence C in bool the carrier of Y ; :: thesis: verum

end;

then reconsider G = { F where F is Subset of Y : ( F is closed & x in F ) } as Subset-Family of Y ;

now :: thesis: for C being set st C in G holds
MaxADSet x c= C

let C be set ; :: thesis: ( C in G implies MaxADSet x c= C )
assume C in G ; :: thesis: MaxADSet x c= C
then ex F being Subset of Y st
( F = C & F is closed & x in F ) ;
hence MaxADSet x c= C by Th23; :: thesis: verum

end;

hence MaxADSet x c= meet { F where F is Subset of Y : ( F is closed & x in F ) } by SETFAM_1:5, A1; :: thesis: verum