input: Write a function to find the intersection of two lists.
  assert intersection([1, 2, 3], [3, 4, 5]) == [3]
  assert intersection([10, 20, 30], [15, 20, 35]) == [20]
  assert intersection([5, 6, 7, 8], [8, 9, 10, 11]) == [8]
output: def intersection(list1, list2):
      return list(set(list1) & set(list2))