reserve i,j for Nat;

theorem
  for A,B being Matrix of REAL st len A=len B & width A=width B & B - A
  = B holds A=0_Rmatrix(len A,width A)
proof
  let A,B be Matrix of REAL;
  assume that
A1: len A=len B & width A=width B and
A2: B - A = B;
  MXR2MXF B + (MXR2MXF A) = MXR2MXF B by A1,A2,MATRIX_4:22;
  hence thesis by A1,MATRIX_4:6;
end;
