  We describe a general approach to modeling rational decision-making agents
who adopt either quantum or classical mechanics based on the Quantum Bayesian
(QBist) approach to quantum theory. With the additional ingredient of a scheme
by which the properties of one agent may influence another, we arrive at a
flexible framework for treating multiple interacting quantum and classical
Bayesian agents. We present simulations in several settings to illustrate our
construction: quantum and classical agents receiving signals from an exogenous
source, two interacting classical agents, two interacting quantum agents, and
interactions between classical and quantum agents. A consistent treatment of
multiple interacting users of quantum theory may allow us to properly interpret
existing multi-agent protocols and could suggest new approaches in other areas
such as quantum algorithm design.
