“…Well-posedness of the Hamilton-Jacobi equation above in the framework of viscosity solutions has recently been established in a large class of metric spaces called geodesic spaces [3,11,14,12,29,30]; see also well-posedness results and applications on networks [34,1,18,35,16,17,7]. A metric space (X, d) is said to be geodesic if for any x, y ∈ X, there exists a geodesic γ t (t ∈ [0, 1]) in X joining x, y with a constant speed; in other words, we have γ 0 = x, γ 1 = y and d(γ s , γ t ) = |s − t|d(x, y) for any s, t ∈ [0, 1].…”