Figure 3:

Regular equilibria trajectories in V_S × I phase space and S × I phase space for S(∞) ∈ [0, 1], I(∞) = V(∞) = 0, when σ(c) = max (1 − 4c, 0). The black curve from Fig. 2 corresponding to S = 0 is the least upper bound on the observed orbits; larger values of I for given V_S are unreachable. Orbits passing through the gap labelled “Fan” exist, but must be constructed using singular controls. The absence of intersecting trajectories in S × I space which would represent shocks and folds will be indicative of a unique Nash equilibrium for the infinite-horizon initial-value problem.