∀ {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} {t₁ t₂ : Std.DTreeMap.Raw α β cmp} {δ : Type w}
  {m : Type w → Type w'} [Std.TransCmp cmp] [inst : Monad m] [LawfulMonad m] {b : δ}
  {f : (a : α) × β a → δ → m (ForInStep δ)}, t₁.WF → t₂.WF → t₁.Equiv t₂ → forIn t₁ b f = forIn t₂ b f