 reserve f,g for Function;
 reserve R for non empty reflexive RelStr;
 reserve R for non empty RelStr;

theorem :: Theorem 4.1 c)
  for R being Approximation_Space
  for x being Subset of R holds
    (f_0 R).x is exact
  proof
    let R be Approximation_Space;
    let x be Subset of R;
    (f_0 R).x = (UAp R).x by UApF0
       .= UAp x by ROUGHS_2:def 11;
    hence thesis;
  end;
