let G be _Graph; :: thesis: ( G is connected implies for v being Vertex of G holds G .reachableFrom v = the_Vertices_of G )
assume A1: G is connected ; :: thesis: for v being Vertex of G holds G .reachableFrom v = the_Vertices_of G
let v be Vertex of G; :: thesis: G .reachableFrom v = the_Vertices_of G

now

let x be set ; :: thesis: ( ( x in G .reachableFrom v implies x in the_Vertices_of G ) & ( x in the_Vertices_of G implies x in G .reachableFrom v ) )
thus ( x in G .reachableFrom v implies x in the_Vertices_of G ) ; :: thesis: ( x in the_Vertices_of G implies x in G .reachableFrom v )
assume x in the_Vertices_of G ; :: thesis: x in G .reachableFrom v
then consider W being Walk of G such that
A2: W is_Walk_from v,x by A1, Def1;
thus x in G .reachableFrom v by A2, Def5; :: thesis: verum

end;

hence G .reachableFrom v = the_Vertices_of G by TARSKI:2; :: thesis: verum