Goal:
    A : Type  P : A → Type  Q : A → Type  Hl' : All Q []
  ============================
   (let H := CoreTactics.block in All (λ x : A, P x × Q x) [])


DEBUG:Going to execute:
match id' with
           | id => idtac
           | _ => revert id'; CoreTactics.revert_until id
           end