∀ {m : Type w → Type w'} {α₁ β₁ : Type w} [inst : Std.Iterator α₁ m β₁] {α₂ β₂ : Type w} [inst_1 : Std.Iterator α₂ m β₂]
  {it : Std.IterM m (β₁ × β₂)},
  it.internalState.memoizedLeft = none →
    ∀ {it' : Std.IterM m β₁},
      it.internalState.left.IsPlausibleStep (Std.IterStep.skip it') →
        Std.Iterators.Types.Zip.PlausibleStep it
          (Std.IterStep.skip
            { internalState := { left := it', memoizedLeft := none, right := it.internalState.right } })