A possible implementation of insertion sort is given by the following Python code: def insertion_sort (xs, key-identity): for i in range(1, len (xs)): e = xs [1] k = key (e) j=i-1 while j> -1 and key (xs [j]) > k: xs [j+1] = xs [j] j= j - 1 xs [j+1] = e Rigorously prove that the worst-case asymptotic time complexity of this insertion sort is T(n) = (n).