∀ {α β γ : Type u_5} {x : Option α} {g : α → Option β} {p : β → Prop} {f : (b : β) → p b → γ}
  (H : ∀ (a : β), x >>= g = some a → p a) (H' : ∀ (a : α), ∀ b ∈ g a, b ∈ x >>= g),
  Option.pmap f (x >>= g) H = do
    let a ← x
    Option.pmap f (g a) ⋯