reserve n for non zero Nat,
  j,k,l,m for Nat,
  g,h,i for Integer;

theorem
  for h,i be Integer st ( h >= 0 & i >= 0 or h < 0 & i < 0 ) & h,i
  are_congruent_mod 2 to_power n holds 2sComplement(n,h) = 2sComplement(n,i)
proof
  let h,i be Integer such that
A1: h >= 0 & i >= 0 or h < 0 & i < 0 and
A2: h,i are_congruent_mod 2 to_power n;
  h mod 2 to_power n = i mod 2 to_power n by A2,NAT_D:64;
  hence thesis by A1,Lm5,Lm6;
end;
