theorem
Std.Iterators.Iter.step_uLift
{α β : Type u}
[Iterator α Id β]
{it : Iter β}
:
it.uLift.step = match it.step with
| ⟨IterStep.yield it' out, h⟩ => PlausibleIterStep.yield it'.uLift { down := out } ⋯
| ⟨IterStep.skip it', h⟩ => PlausibleIterStep.skip it'.uLift ⋯
| ⟨IterStep.done, h⟩ => PlausibleIterStep.done ⋯