reserve x for object,
  a,b for Real,
  k,k1,i1,j1,w for Nat,
  m,m1,n,n1 for Integer;
reserve p,q for Rational;

theorem Th20:
  numerator(p) = denominator(p) iff p = 1
proof
  hereby
    assume numerator(p)=denominator(p);
    then numerator(p)/denominator(p)=1 by XCMPLX_1:60;
    hence p=1 by Th12;
  end;
  thus thesis;
end;
