0 = 0
        1 = 1
    0 + 1 = 1
    1 + 2 = 3
2 + 3 + 4 = 9

        0 = 0
        1 = 1
    0 + 1 = 1
    1 + 2 = 3
2 + 3 + 4 = 9

        0 = 0
        1 = 1
    0 + 1 = 1
    1 + 2 = 3
2 + 3 + 4 = 9

        0 = 0
        1 = 1
    0 + 1 = 1
    1 + 2 = 3
2 + 3 + 4 = 9

List() = concat(List())
List() = concat(List(List()))
List() = concat(List(List(), List()))
List() = concat(List(List(), List(), List()))
List(1, 2, 3, 4, 5, 6) = concat(List(List(1, 2, 3, 4, 5, 6)))
List(1, 2, 3, 4, 5, 6) = concat(List(List(1, 2, 3, 4, 5, 6), List()))
List(1, 2, 3, 4, 5, 6) = concat(List(List(1, 2, 3), List(4, 5, 6)))
List(1, 2, 3, 4, 5, 6) = concat(List(List(), List(1, 2, 3, 4, 5, 6)))
List(1, 2, 3, 4, 5, 6) = concat(List(List(1, 2, 3, 4, 5, 6), List(), List()))
List(1, 2, 3, 4, 5, 6) = concat(List(List(1, 2, 3, 4, 5), List(6), List()))
List(1, 2, 3, 4, 5, 6) = concat(List(List(1, 2, 3), List(4, 5, 6), List()))
List(1, 2, 3, 4, 5, 6) = concat(List(List(1), List(2, 3, 4, 5, 6), List()))
List(1, 2, 3, 4, 5, 6) = concat(List(List(), List(1, 2, 3, 4, 5, 6), List()))
List(1, 2, 3, 4, 5, 6) = concat(List(List(), List(1, 2, 3, 4, 5), List(6)))
List(1, 2, 3, 4, 5, 6) = concat(List(List(), List(1, 2, 3), List(4, 5, 6)))
List(1, 2, 3, 4, 5, 6) = concat(List(List(), List(1), List(2, 3, 4, 5, 6)))
List(1, 2, 3, 4, 5, 6) = concat(List(List(), List(), List(1, 2, 3, 4, 5, 6)))
List(1, 2, 3, 4, 5, 6) = concat(List(List(1, 2), List(3, 4), List(5, 6)))

List() = zipFun(List(),List())
List() = zipFun(List(),List(a, b, c))
List() = zipFun(List(1, 2, 3),List())
List((1,a)) = zipFun(List(1),List(a))
List((1,a)) = zipFun(List(1),List(a, b, c))
List((1,a)) = zipFun(List(1, 2, 3),List(a))
List((1,a), (2,b)) = zipFun(List(1, 2),List(a, b))
List((1,a), (2,b)) = zipFun(List(1, 2),List(a, b, c))
List((1,a), (2,b)) = zipFun(List(1, 2, 3),List(a, b))
List((1,a), (2,b), (3,c)) = zipFun(List(1, 2, 3),List(a, b, c))

List() = heads(List())
List() = heads(List(List()))
List() = heads(List(List(), List()))
List() = heads(List(List(), List(), List()))
List(1) = heads(List(List(1, 2, 3, 4, 5, 6)))
List(1) = heads(List(List(1, 2, 3, 4, 5, 6), List()))
List(1) = heads(List(List(), List(1, 2, 3, 4, 5, 6)))
List(1) = heads(List(List(1, 2, 3, 4, 5, 6), List(), List()))
List(1) = heads(List(List(), List(1, 2, 3, 4, 5, 6), List()))
List(1) = heads(List(List(), List(), List(1, 2, 3, 4, 5, 6)))
List(1, 2) = heads(List(List(1), List(2, 3, 4, 5, 6), List()))
List(1, 2) = heads(List(List(), List(1), List(2, 3, 4, 5, 6)))
List(1, 4) = heads(List(List(1, 2, 3), List(4, 5, 6)))
List(1, 4) = heads(List(List(1, 2, 3), List(4, 5, 6), List()))
List(1, 4) = heads(List(List(), List(1, 2, 3), List(4, 5, 6)))
List(1, 6) = heads(List(List(1, 2, 3, 4, 5), List(6), List()))
List(1, 6) = heads(List(List(), List(1, 2, 3, 4, 5), List(6)))
List(1, 3, 5) = heads(List(List(1, 2), List(3, 4), List(5, 6)))

List() = heads(List())
List() = heads(List(List()))
List() = heads(List(List(), List()))
List() = heads(List(List(), List(), List()))
List(1) = heads(List(List(1, 2, 3, 4, 5, 6)))
List(1) = heads(List(List(1, 2, 3, 4, 5, 6), List()))
List(1) = heads(List(List(), List(1, 2, 3, 4, 5, 6)))
List(1) = heads(List(List(1, 2, 3, 4, 5, 6), List(), List()))
List(1) = heads(List(List(), List(1, 2, 3, 4, 5, 6), List()))
List(1) = heads(List(List(), List(), List(1, 2, 3, 4, 5, 6)))
List(1, 2) = heads(List(List(1), List(2, 3, 4, 5, 6), List()))
List(1, 2) = heads(List(List(), List(1), List(2, 3, 4, 5, 6)))
List(1, 4) = heads(List(List(1, 2, 3), List(4, 5, 6)))
List(1, 4) = heads(List(List(1, 2, 3), List(4, 5, 6), List()))
List(1, 4) = heads(List(List(), List(1, 2, 3), List(4, 5, 6)))
List(1, 6) = heads(List(List(1, 2, 3, 4, 5), List(6), List()))
List(1, 6) = heads(List(List(), List(1, 2, 3, 4, 5), List(6)))
List(1, 3, 5) = heads(List(List(1, 2), List(3, 4), List(5, 6)))

f (x) = Prod(Var(x), Var(x))
f'(x) = Sum(Prod(Var(x), Number(1)), Prod(Var(x), Number(1)))

f (x) = x * x
f'(x) = x * 1 + x * 1
g (x) = 2 * x * x + 3 * x
g'(x) = 2 * x * 1 + x * (2 * 1 + x * 0) + 3 * 1 + x * 0
g (3) = 27
g'(3) = 15

ta(x) = x + 3
tb(x) = x + 3
tc(x) = x + 3
td(x) = x + 3
te(x) = 2 * x + 3
tf(x) = 2 * x + 3
tg(x) = 6 * x
th(x) = x^6

f4(x) = x^4 + 7 * x^3 + 20 * x^2 + 23 * x + 5
f3(x) = 4 * x^3 + 21 * x^2 + 40 * x + 23
f2(x) = 12 * x^2 + 42 * x + 40
f1(x) = 24 * x + 42
f0(x) = 24

f4(0) = 5 ok
f4(1) = 56 ok
f4(2) = 203 ok
f4(3) = 524 ok
f4(4) = 1121 ok

f3(0) = 23 ok
f3(1) = 88 ok
f3(2) = 219 ok
f3(3) = 440 ok

f2(0) = 40 ok
f2(1) = 94 ok
f2(2) = 172 ok

f1(0) = 42 ok
f1(1) = 66 ok

f0(0) = 24 ok