Incorrect. What if B is [ ]? Then tail(B)
makes no sense.
Incorrect. What if B = [2,4,6]? The equation says that
merge([ ], [2,4,6]) = merge([2,4,6], [4,6]). If the recursive
call to merge is assumed to be correct, that is [2,4,4,6,6].
But merge([ ], [2,4,6]) is supposed to be [2,4,6].