in epidemiology. Global stability of the endemic equilibrium states of these systems is
established. … Korobeinikov and Wake [5] found a symmetric-in-variables Lyapunov
function, which was later extended to a wider range of epidemic models, including models
with a larger number of compartments [6], [7], [8], [9] and models with non-linear functional
responses [10], [11], [12], [13], [14], [15], [16]. In this paper, we construct a Lyapunov function …