reserve x,y,z for Real,
  a,b,c,d,e,f,g,h for Nat,
  k,l,m,n,m1,n1,m2,n2 for Integer,
  q for Rational;

theorem Th15:
  a divides 1 implies a=1
proof
  assume
A1: a divides 1;
  then a divides 1+1 by NAT_D:8;
  hence thesis by A1,NEWTON:39;
end;
