B.3 BOOLE

Boolean Properties of Sets by Library Committee

1 for X being set holds X \/ {} = X;

2 for X being set holds X /\ {} = {};

3 for X being set holds X \ {} = X;

4 for X being set holds {} \ X = {};

5 for X being set holds X \+\ {} = X;

6 for X being set st X is empty holds X = {};

7 for x, X being set st x in X holds X is non empty;