  Exponential error bounds achievable by universal coding and decoding are
derived for frame-asynchronous discrete memoryless %asynchronous multiple
access channels with two senders, via the method of subtypes, a refinement of
the method of types. Maximum empirical multi-information decoding is employed.
A key tool is an improved packing lemma, that overcomes the technical
difficulty caused by codeword repetitions, via an induction based new argument.
The asymptotic form of the bounds admits numerical evaluation. This demostrates
that error exponents achievable by synchronous transmission (if possible) can
be superseeded via controlled asynchronism, i.e. a deliberate shift of the
codewords.
