 reserve X, Y for set, A for Ordinal;
 reserve z,z1,z2 for Complex;
 reserve r,r1,r2 for Real;
 reserve q,q1,q2 for Rational;
 reserve i,i1,i2 for Integer;
 reserve n,n1,n2 for Nat;

theorem
  [i1,i1+i] in addRel(INT,i)
proof
  i1 in INT & i1+i in INT by INT_1:def 2;
  hence thesis by Th11;
end;
