reserve
  a for natural Number,
  k,l,m,n,k1,b,c,i for Nat,
  x,y,z,y1,y2 for object,
  X,Y for set,
  f,g for Function;

theorem Th7:
  for a,c being natural Number holds
  c <= a implies Seg c = Seg a /\ Seg c by Th5,XBOOLE_1:28;
