English: In general, permissively licensed code is forward compatible with any other license type. However, only permissive licenses, such as the BSD and MIT, can feed into other permissive licenses. Restrictive licenses like the GPL are backward compatible with themselves and permissive licenses, but must adopt the restrictive license from then on. Proprietary licenses can incorporate upstream permissively licensed code, but by definition are incompatible with any other downstream license. Grey represents actions that are not permitted without negotiating a separate license agreement with the rights owner.