reserve r,t for Real;
reserve i for Integer;
reserve k,n for Nat;
reserve p for Polynomial of F_Real;
reserve e for Element of F_Real;
reserve L for non empty ZeroStr;
reserve z,z0,z1,z2 for Element of L;

theorem Th2:
  for a,b being Real st |.a.| = b holds a = b or a = -b
  proof
    let a be Real;
    |.a.| = a or |.a.| = -a by COMPLEX1:71;
    hence thesis;
  end;
