reserve
  j, k, l, n, m, t,i for Nat,
  K for comRing, 
  a for Element of K,
  M,M1,M2 for Matrix of n,m,K,
  pK,qK for FinSequence of K,
  A for Matrix of n,K;

theorem Th1:
  for K being non empty set
  for M1,M2 being Matrix of n,m,K holds width M1 = width M2
proof
  let K be non empty set;
  let M1,M2 be Matrix of n,m,K;
  per cases;
  suppose
A1: n > 0;
    then width M1 = m by MATRIX_0:23;
    hence thesis by A1,MATRIX_0:23;
  end;
  suppose
A2: n=0;
    then width M1 = 0 by MATRIX_0:22;
    hence thesis by A2,MATRIX_0:22;
  end;
end;
