A greenlist is a non-empty list of pairs of integers where a pair of integers is a list of exactly two integer and where each pair ( x y) has the property that y x = 1.

Example: ( ( 5 6) ( 3 4) ( 2 3) ( -5 -4) ) is a greenlist.

The following items are not greenlists:

( ( 4 7) ( 9 10 ) ) , ( ( 4.5 5.5) ( 7 8) ) , ( ) ,

( ( 2 4 6) ( 5 6) ( 1 2)) , ( 3 4 5 6) , "green apples"

Write a Scheme predicate, ( greenlist? z) , hat returns #t if z is a greenlist; otherwise return #f. Check ALL conditions. Test your function on all of the above examples. [Hint: Create helper functions. ]