have foo := Function.iterate_cancel sorry heq
case left.hm.inr
a b : ℕ
heq : next^[a] (0, 0) = next^[b] (0, 0)
h✝ : (0, 0) ∉ Function.periodicPts next
⊢ a < 0
case left.hm.inr
a b : ℕ
heq : next^[a] (0, 0) = next^[b] (0, 0)
h✝ : (0, 0) ∉ Function.periodicPts next
foo : next^[a - b] (0, 0) = (0, 0)
⊢ a < 0