Write PROLOG programs
1. To add an element to a list provided it is not present in the list.
2. To delete first occurrence of an element from a list.
3. To delete all occurrences of an element from a list.
4. *To remove the first occurrence of an element X in L with Y giving the result in L1.
5. *To substitute all occurrences of an element by another element in a list.
6. To determine whether a list is a sub list of another list.
A list is a sub list of another list if it’s elements are present in another list consecutively and in the same order.
7. To determine whether an element is a member of a set.
8. *To determine whether a set is a subset of another set.
9. To determine intersection of two sets.
10. To determine union of two sets.
11. To determine difference of two sets.
12. *To determine symmetric difference of two sets.
13. *To delete nth element in L, leaving the rest in L1.
14. *To replace nth element by another element X in L, leaving the resultant list in L1.
