Exercises
lCan you give an equation defining a function pairs, such that
pairs(L, M) creates a list in which each element of L is paired with each element of M, e.g.
pairs([1, 2, 3], [4, 5, 6])
   ==> [ [1, 4],  [1, 5],  [1, 6],
          [2, 4], [2, 5], [2, 6],
         [3, 4], [3, 5], [3, 6] ]