reserve G,G1,G2 for _Graph;
reserve e,x,y for set;
reserve v,v1,v2 for Vertex of G;
reserve W for Walk of G;

theorem
  (ex v1 being Vertex of G st for v2 being Vertex of G ex W being Walk
  of G st W is_Walk_from v1,v2) implies G is connected by Lm6;
