Pre: Crib map_{left,right} for Either.
Pre: Crib map_{left,right} for Either.

ncalexan/datomish,ncalexan/mentat,mozilla/mentat,mozilla/mentat,mozilla/mentat,mozilla/mentat,ncalexan/mentat,mozilla/mentat,ncalexan/mentat,mozilla/mentat,ncalexan/datomish,ncalexan/mentat,ncalexan/mentat,ncalexan/mentat