append :: b → b → b
cons :: a → b → b
map :: (a → a) → b → b
nil :: b
append(nil, X) → X
append(cons(Y, V), U) → cons(Y, append(V, U))
map(I, nil) → nil
map(J, cons(X1, Y1)) → cons(J(X1), map(J, Y1))
append(append(U1, V1), W1) → append(U1, append(V1, W1))
map(J1, append(X2, Y2)) → append(map(J1, X2), map(J1, Y2))