conv =>
  right; rw [isSome_iff_exists]; congr
  intro; unfold constrRun; rw [pbind_eq_some]
case some
α qs : Type
M : DFA α qs
w : Word { x // x ∈ M.Z }
q : { x // x ∈ M.Q }
x : { x // x ∈ M.Z }
xs : List { x // x ∈ M.Z }
q' : { x // x ∈ M.Q }
hq' : M.δ (q, x) = some q'
⊢ Option.isSome (del_star_curried M (x :: xs) q) = true ↔ Option.isSome (constrRun (x :: xs) q) = true
case some
α qs : Type
M : DFA α qs
w : Word { x // x ∈ M.Z }
q : { x // x ∈ M.Q }
x : { x // x ∈ M.Z }
xs : List { x // x ∈ M.Z }
q' : { x // x ∈ M.Q }
hq' : M.δ (q, x) = some q'
⊢ Option.isSome (del_star_curried M (x :: xs) q) = true ↔
    ∃ x_1 z,
      ∃ (H : z ∈ M.δ (q, x)),
        (do
            let r' ← constrRun xs z
            some (NFA.Run.step q ⋯ r' ⋯)) =
          some x_1