exists (λ e => e.casesOn)
case h₀.Pure.refl
C : _root_.Container
R : Type u₁
x y : R
⊢ ∃ k₁ k₂,
    M.destruct (construct (Functor.Pure x)) = { fst := A.Pure x, snd := k₁ } ∧
      M.destruct (construct (Functor.Pure x)) = { fst := A.Pure x, snd := k₂ } ∧
        ∀ (i : Container.B (Container C R) (A.Pure x)), eq (k₁ i) (k₂ i)
case h₀.Pure.refl
C : _root_.Container
R : Type u₁
x y : R
⊢ ∃ k₂,
    M.destruct (construct (Functor.Pure x)) =
        { fst := A.Pure x, snd := fun e => PEmpty.casesOn (fun x => M (Container C R)) e } ∧
      M.destruct (construct (Functor.Pure x)) = { fst := A.Pure x, snd := k₂ } ∧
        ∀ (i : Container.B (Container C R) (A.Pure x)),
          eq ((fun e => PEmpty.casesOn (fun x => M (Container C R)) e) i) (k₂ i)