Coding for write-unidirectional memories and conflict resolution

Write-unidirectional memories (WUMs) have been introduced recently. They are binary storage devices having a close relationship to write-once memories (WOMs). When updating the information stored by a WUM the encoder can write 1 's to some positions of the WUM or O's to some positions of the WUM but it is not allowed to do both at the same time. Wolf, Wyner, Ziv and Korner investigated WOMs in the four cases arising if the encoder and/or the decoder is informed/uninformed about the previous state of the memory. We investigate the WUMs under these circumstances. We mostly deal with the two cases when the encoder is uninformed, and give bounds and conjectures on the best achievable rates. In the last part, we discuss a related combinatorial problem: conflict resolution on a multiple access channel.