Lists of Lists
lIn order to keep track of, or manage, an arbitrary collection of lists, we can use lists with lists as elements
lList of pairs: [ [1, 2], [3, 4], [5, 6]]
lThe ordering within each pair can be respected or not, as we desire (ordered
vs. unordered pair)
lList of triples: [[1, 2, 3], [4, 5, 6]]
lList of assorted-size lists:
[[1, 2, 3], [2, 3], [3], []]
[[1, 2, 3], [2, 3], [3], []]