∀ {α β : Type w} [inst : Std.Iterator α Id β] [inst_1 : Std.Iterators.Finite α Id] {m : Type x → Type x'}
  [inst_2 : Monad m] [LawfulMonad m] [inst_4 : Std.IteratorLoop α Id m] [Std.LawfulIteratorLoop α Id m]
  [inst_6 : Std.LawfulDeterministicIterator α Id] {γ : Type x} {it : Std.Iter β} {init : γ}
  {f : (out : β) → out ∈ it.toList → γ → m (ForInStep γ)},
  forIn' it.toList init f = forIn' it init fun out h acc => f out ⋯ acc