proposer une version recursive du programme suivant:
def foo(L1, L2):
res = []
while L1 != [] and L2 != []:
if L1[0] < L2[0]:
res.append(L1[0])
L1 = L1[1:]
else:
res.append(L2[0])
L2 = L2[1:]

if L1 == []:
res = res + L2
else:
res = res + L1

return res