But , ( 2A , - 1M ) and ( - 1A , 2M ) can be traded into non-negative portfolios .
This means that ( 1A , - 1M ) and ( - 1A , 1M ) can not be exchanged into non-negative portfolios .
( 2A , - 1M ) and ( - 1A , 2M ) can be traded into non-negative portfolios .
This means that ( 1A , - 1M ) and ( - 1A , 1M ) can not be exchanged into non-negative portfolios .