code: def mcons(self, iterable):
          
          head = self
          for elem in iterable:
              head = head.cons(elem)
  
          return head
docs: Return a new list with all elements of iterable repeatedly cons:ed to the current list.
          NB! The elements will be inserted in the reverse order of the iterable.
          Runs in O(len(iterable)).
  
          >>> plist([1, 2]).mcons([3, 4])
          plist([4, 3, 1, 2])