reserve i,j,k,l for natural Number;
reserve A for set, a,b,x,x1,x2,x3 for object;
reserve D,D9,E for non empty set;
reserve d,d1,d2,d3 for Element of D;
reserve d9,d19,d29,d39 for Element of D9;
reserve p,q,r for FinSequence;
reserve s for Element of D*;

theorem Th99:
  <*d1,d2*> in 2-tuples_on D
proof
  <*d1,d2*> in the set of all
 <*c1,c2*> where c1 is (Element of D), c2 is Element of D;
  hence thesis by Th97;
end;
