4041: Algorithms and Data St The Python function mergesort is shown below. It recursively sorts a list of numbers u using a recursive divide- and-conquer algorithm, then returns a sorted list s. The function head returns the first element of a nonempty list Q, and the function tail returns all but the first element of a nonempty list o. Lines 06-07 detect if u is trivially sorted. Lines 09-16 split U into two halves, L and R, of approximately equal lengths. Lines 17-18 recursively sort L and R. Lines 19-28 merge the sorted L and R back into a sorted list s. 01 def head (Q): 02 return Qt0] 03 def tail(Q): 04 return Qi1:] 05 def mergesort(U): 06 if U[1 or tail(U)[ 07 08 else: 09 10 R[ 11 while U - [ and tail(U) - [: 12 13 return U L = L + [head (U) ] U-tail (U) R R [head (U) ] Utail(U) 15 16 17 18 19 20 while L - [1 and R L LU L = mergesort (L) Rmergesort (R) [1: head (R): head (L) Shead (L) 1 L tail(L) if