  This paper proposes a general optimization framework for rate splitting
multiple access (RSMA) in beyond diagonal (BD) reconfigurable intelligent
surface (RIS) assisted ultra-reliable low-latency communications (URLLC)
systems. This framework can provide a suboptimal solution for a large family of
optimization problems in which the objective and/or constraints are linear
functions of the rates and/or energy efficiency (EE) of users. Using this
framework, we show that RSMA and RIS can be mutually beneficial tools when the
system is overloaded, i.e., when the number of users per cell is higher than
the number of base station (BS) antennas. Additionally, we show that the
benefits of RSMA increase when the packets are shorter and/or the reliability
constraint is more stringent. Furthermore, we show that the RSMA benefits
increase with the number of users per cell and decrease with the number of BS
antennas. Finally, we show that RIS (either diagonal or BD) can highly improve
the system performance, and BD-RIS outperforms regular RIS.
