theorem Th42:
  for a being non zero Real holds
  symmetric_3(1/a,1/a,-1/a,0,0,0) * symmetric_3(a,a,-a,0,0,0) = 1.(F_Real,3)
  proof
    let a be non zero Real;
    reconsider b = 1 / a as non zero Real;
    1 / b = a by XCMPLX_1:56;
    hence thesis by Th41;
  end;
