reserve i,j for Nat;

theorem Th44:
  for K being Ring,M1,M2 being Matrix of K st len M1=len M2 &
  width M1=width M2 holds - M1 - M2 = - M2 - M1
proof
  let K be Ring,M1,M2 be Matrix of K;
  assume len M1=len M2 & width M1=width M2;
  then
A1: len (-M2)=len M1 & width (-M2)=width M1 by MATRIX_3:def 2;
  len (-M1)=len M1 & width (-M1)=width M1 by MATRIX_3:def 2;
  hence thesis by A1,MATRIX_3:2;
end;
