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;
