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

In 1981 Jahn used the elimination technique of the first author to determine the average errors capacity region of an arbitrarily varying multiple-access channel (AVMAC), when this region has a nonempty interior. Here we remove this restriction. In his thesis (1990), Gubner (1990) missed this result because he used the first author's first approach to the MAC, which is based on conditional decoding, and not the first author's second approach, which is based on maximum likelihood decoding. This second approach was originally needed for a kind of compound MAC. For the AVMBC the difference between the approaches is naturally even more essential.