1. countdown Example: countdown(5,[5,4,3,2,1]).
NOTE - your function should be able to answer questions such as: ?- countdown(5,L).
2. count_occur Example: count_occur(7,[5,2,6,7,8,7,0],2).
the list [5,2,6,7,8,7,0] has 2 occurences of 7
3. array insert Example: ains([0,0,1,1,2,2],4,53,[0,0,1,1,53,2,2]).
and array get Example: aget([0,0,1,1,53,2,2],4,53).
These functions simulate array operations, using lists. "ains" takes a list, an index, and a value to insert, and produces a list with the value inserted at the index point. "aget" takes a list and an index, and produces the value from the list at the index point.