cons :: nat → list → list
explode :: list → (nat → nat) → nat → nat
implode :: list → (nat → nat) → nat → nat
nil :: list
op :: (nat → nat) → (nat → nat) → nat → nat
op(F, G, X) → F(G(X))
implode(nil, F, X) → X
implode(cons(H, T), F, X) → implode(T, F, F(X))
explode(nil, F, X) → X
explode(cons(H, T), F, X) → explode(T, op(F, F), F(X))