comp :: (c → c) → (c → c) → c → c
cons :: a → b → b
map :: (a → a) → b → b
nil :: b
twice :: (c → c) → c → c
map(F, nil) → nil
map(Z, cons(U, V)) → cons(Z(U), map(Z, V))
comp(I, J, X1) → I(J(X1))
twice(Z1) → comp(Z1, Z1)