Nondeterministic Behaviours in Double Categorical Systems Theory

Abstract: In this paper, we build a double theory capturing the idea of nondeterministic behaviours and trajectories. Following Jaz Myers' Double Categorical Systems Theory, we construct a monoidal double category of systems and interfaces, which then yields (co)representable behaviours. We use conditional products in Markov categories to get compositional trajectories and behaviours, and represent nondeterministic systems and lenses using parametric deterministic maps. The resulting theory can also represent imprecise probability via naming Knightian choices, \emph{`a la} Liell-Cock and Staton.