Don't really know, unfortunately!

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Initially, codesharing will be offered between the United States and Vietnam via Paris and Tokyo, with American placing its ``AA'' designator code on Vietnam Airlines' flights between Paris and both Hanoi and Ho Chi Minh City and between Tokyo and both Vietnamese cities. Under the arrangement, Vietnam Airlines will place its ``VN'' designator code on American's U.S.-Paris and U.S.-Tokyo flights.

In later phases, codesharing will be offered via other Pacific gateways and the airlines will also codeshare on some of each other's domestic routes.

http://biz.yahoo.com/prnews/010720/daf012.html