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
  for G1 being non _trivial connected _Graph, v being Vertex of G1, G2
  being removeVertex of G1,v st v is endvertex holds G2 is connected by Lm5;
