J-I.Fujii, R.Nakamoto and K.Yanagi, Concavity of the aux-iliary function appearing in quantum reliability function, IEEE Trans. Information Theory, vol IT-52, no 7, pp 3310-3313, 2006.
S.Furuichi, K.Yanagi and K.Kuriyama, A sufficient condi-tion on concavity of the auxiliary function appearing in quantum reliability function, Information, vol 6, no 1, pp 71-76, 2003.