∀ {α β β' : Type w} {m : Type w → Type w'} [inst : Std.Iterator α m β] [inst_1 : Monad m]
  [inst_2 : Std.IteratorLoop α m m] [Std.Iterators.Finite α m] [LawfulMonad m] [Std.LawfulIteratorLoop α m m]
  {it : Std.IterM m β} {f : β → β'}, (Std.IterM.map f it).length = it.length