Python programming help, please.

Write a function def mergeSorted(a, b) that merges two sorted lists, producing a new sorted list. Keep an index into each list, indicating how much of it has been processed already. Each time, append the smallest unprocessed element from either list, then advance the index. For example,

if a is: 1 4 9 16 and b is: 4 7 9 9 11

then mergeSorted returns a new list containing the values: 1 4 4 7 9 9 9 11 16 Finally, write the main program to call the function to merge two already sorted lists.