theorem :: Proposition 6 b)
  Y c= Z implies (CMap kap).(X,Z) <= (CMap kap).(X,Y)
  proof
    assume Y c= Z; then
    1 - kap.(X,Y) >= 1 - kap.(X,Z) by XREAL_1:10,ROUGHIF1:def 8; then
    (CMap kap).(X,Y) >= 1 - (kap).(X,Z) by CDef;
    hence thesis by CDef;
  end;
