type S = List(Char)

!!! x == "hi"
x : S
x = "hi"

type T(a) = Unit + a * T(a) * T(a)

leaf : T(a)
leaf = left(unit)

testT : T(N)
testT = right(3, right(4, right(1, leaf, leaf), right(6, leaf, leaf)), right(9, leaf, leaf))

!!!  mirror(mirror(testT)) == testT
mirror : T(a) -> T(a)
mirror(left(unit)) = left(unit)
mirror(right(a,l,r)) = right(a, mirror(r), mirror(l))