reserve a,b,i,k,m,n for Nat;
reserve s,z for non zero Nat;
reserve r for Real;
reserve c for Complex;
reserve e1,e2,e3,e4,e5 for ExtReal;

theorem Th14:
  for i,j being Integer st i,j are_coprime holds
  i <> j or i = j = 1 or i = j = -1
  proof
    let i,j be Integer;
A1: i gcd i = |.i.| by INT_5:12;
    |.i.| = i or |.i.| = -i by ABSVALUE:1;
    hence thesis by A1;
  end;
