 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 Prop2b: ::: Proposition 2 b)
  X <> {} implies (kappa (X,Y) = 0 iff X misses Y)
  proof
    assume
AA: X <> {};
    thus kappa (X,Y) = 0 implies X misses Y by LemmaProp2b;
    assume X misses Y; then
    card (X /\ Y) / card X = 0;
    hence thesis by AA,KappaDef;
  end;
