  The tightest and most robust cosmological results of the next decade will be
achieved by bringing together multiple surveys of the Universe. This endeavor
has to happen across multiple layers of the data processing and analysis, e.g.,
enhancements are expected from combining Euclid, Rubin, and Roman (as well as
other surveys) not only at the level of joint processing and catalog
combination, but also during the post-catalog parts of the analysis such as the
cosmological inference process. While every experiment builds their own
analysis and inference framework and creates their own set of simulations,
cross-survey work that homogenizes these efforts, exchanges information from
numerical simulations, and coordinates details in the modeling of astrophysical
and observational systematics of the corresponding datasets is crucial.
