Good job! Before we wrap this section up, let's have a quick summary and a quiz. What did we learn?

1. Nested lists are lists within lists. They may or may not be rectangular and can consist of as many dimensions as needed, but two-dimensional nested lists are the most popular.
2. To access a specific element in a nested list, use as many square bracket pairs as there are dimensions in the list:

   nested_list = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
   nested_list[1][2] # returns 6

3. To iterate over the values of a nested list, use:

   for row in nested_list:
     for cell in row:
       ...

4. To iterate over the indexes of a nested list, use:

   for i in range(len(nested_list)):
     for j in range(len(nested_list[i])):
       ...

5. To modify the elements of a nested list, iterate over the indexes, not the values.
6. To quickly copy a nested list, use:

   import copy
   new_nested_list = copy.deepcopy(nested_list)

How about that short quiz now?