Arbitrarily varying multiple-access channels. I. Ericson's symmetrizability is adequate, Gubner's conjecture is true

Ericson's conjecture has been established by Csiszar and Narayan (1988). In the theory of identification the cycle closes: both, the non-single letter separability by random words and symmetrizability are used and needed. Gubner extends the decoding rule of Csiszar and Narayan to the multiple-access situation by following "conditional decoding". This is a suboptimal decoding rule, but was suited for the discovery of the capacity theorem for the multiple-access channel (MAC). Its drawback for systems of channels was soon realized by Ahlswede (1974), where for the derivation of the capacity theorem for the compound MAC maximum likelihood decoding could be analysed. For the arbitrarily varying MAC (AVMAC) suboptimality of the conditional decoding rule becomes even more significant. The authors examine if Gubner's conjecture is true.