Type error. L is a list. So [L] is a list holding
one list. We are not allowing lists of lists. All
members of a list are integers.
Incorrect. Suppose that, by head[L] this equation
means head(L) and tail[L] means tail(L).
Suppose L = [2,4,6].
Correct: successors(L) = [3,5,7]. This
equation says that successors(L) = [3,4,6].