 reserve f,g for Function;
 reserve R for non empty reflexive RelStr;
 reserve R for non empty RelStr;
 reserve f for Function of the carrier of R, bool the carrier of R;

theorem :: 4.1 h)
  (f_0 R).{} = {}
  proof
    { u where u is Element of R : (tau R).u meets {}R } c= {}
    proof
      let y be object;
      assume y in { u where u is Element of R : (tau R).u meets {}R };
      then consider u being Element of R such that
A1:   u = y & (tau R).u meets {}R;
      thus thesis by A1;
    end;
    hence thesis by Defff;
  end;
