Terminal leaves in copy-on-write overlay mode

A terminal leaf never consumes an inherited flag. Since a nonempty overlay exposes at least one visible flag, the overlay interface is vacuous for terminal parses.

theorem IndexedGrammar.Aho.overlayScheduleRun_terminal_false {T : Type} {g : IndexedGrammar T} [Fintype g.nt] {A : g.nt} {stack : List g.flag} {a : T} {r : IRule T g.nt g.flag} (hr : r ∈ g.rules) (hlhs : r.lhs = A) (hc : r.consume = none) (hrhs : r.rhs = [IRhsSymbol.terminal a]) : OverlayScheduleRun (NFParse.terminal hr hlhs hc hrhs)

A terminal parse cannot be entered with a nonempty private overlay.