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 G being non _trivial _finite connected _Graph holds ex v1,v2 being
Vertex of G st v1 <> v2 & not v1 is cut-vertex & not v2 is cut-vertex by Lm21;
