01 def head(Q): 02 return Q00] 03 def tail(Q): 04 return Q[1:] 05 def mergesort(U): 06 if U == [ ] or tail(U) -= [ ] : 07 08 else: 09 L=[] 10 R=[] 11 while U != [] and tail(U) != []; 12 13 14 15 16 17 L=mergesort (L) 18R-mergesort(R) return U L = L + [head(U)] RR [head(U)] U = tail(U) 20 while L !- [] and R !- [] 21 head (R): head (L) s - s [head (L)] L = tail(L) if