reserve G,G1,G2 for _Graph;
reserve W,W1,W2 for Walk of G;
reserve e,x,y,z for set;
reserve v for Vertex of G;
reserve n,m for Element of NAT;

theorem Th13:
 for e,x,y being object holds
  e Joins x,y,G implies len G.walkOf(x,e,y) = 3
proof let e,x,y be object;
  assume e Joins x,y,G;
  then G.walkOf(x,e,y) = <*x,e,y*> by Def5;
  hence thesis by FINSEQ_1:45;
end;
