 reserve R for 1-sorted;
 reserve X,Y for Subset of R;
 reserve R for finite 1-sorted;
 reserve X,Y for Subset of R;
 reserve R for finite Approximation_Space;
 reserve X,Y,Z,W for Subset of R;

theorem :: Proposition 4 f)
  kappa_2 (X,Y) = kappa ([#]R, X` \/ Y) =
    kappa ([#]R,X`) + kappa ([#]R, X /\ Y) by Lemma4f1,Lemma4f2;
