“…As always, the tricky part of the optimization work lies at the junction of the two regimes, that is, at the switching point (if any). Most of the existing literature on regime switching focuses on optimal individual (for example, central planner) problems, and thus, it has naturally relied on versions of the Pontryagin optimality conditions, including some specific continuity (or transversality) conditions on the maximized Hamiltonians and, in some cases, also on the co-state variables at the switching points (see, for example, Tomiyama (1985), Boucekkine et al (2013aBoucekkine et al ( ,b, 2020). The same technique has been used to characterize open-loop equilibria in dynamic game models with regime switching (see Boucekkine et al (2011), for a two-country game without pollution irreversibility, in addition to Wagener and de Zeeuw (2021), which does deal with irreversibility).…”