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

theorem Th56:
  Trace (-M1) = -Trace M1
proof
A1: len M1=n & width M1=n by MATRIX_0:24;
  Trace M1+Trace (-M1)=Trace (M1+(-M1)) by Th53
    .=Trace (0.(K,n,n)) by A1,MATRIX_4:2
    .=Trace (0.(K,n))
    .=0.K by Th55;
  hence thesis by RLVECT_1:6;
end;
