reserve i,n for Nat,
  K for Field,
  M1,M2,M3,M4 for Matrix of n,K;

theorem Th59:
  Trace (M1-M2)=Trace M1-Trace M2
proof
  Trace (M1-M2)=Trace M1+Trace (-M2) by Th53
    .=Trace M1+-Trace M2 by Th56;
  hence thesis;
end;
