fact: Definition option_orb {A} (x y : option A) : option A := match x, y with | Some x', _ => Some x' | None, Some y' => Some y' | None, None => None end.
imports: Fiat.Parsers.ContextFreeGrammar.Core Fiat.Parsers.BaseTypes Fiat.Parsers.GenericBaseTypes Fiat.Parsers.GenericRecognizer