 reserve R for finite Approximation_Space;
 reserve X,Y,Z for Subset of R;
 reserve kap for RIF of R;

theorem :: Proposition 6 b) probably will be removed as a consequence
  Y c= Z implies (CMap kappa R).(X,Z) <= (CMap kappa R).(X,Y)
  proof
    assume Y c= Z; then
    1 - kappa (X,Y) >= 1 - kappa (X,Z) by XREAL_1:10, ROUGHIF1:7; then
    1 - (kappa R).(X,Y) >= 1 - kappa (X,Z) by ROUGHIF1:def 2; then
    1 - (kappa R).(X,Y) >= 1 - (kappa R).(X,Z) by ROUGHIF1:def 2; then
    (CMap kappa R).(X,Y) >= 1 - (kappa R).(X,Z) by CDef;
    hence thesis by CDef;
  end;
