“…Indeed, any linear combination αDX H| O 0 (0, 0, 0, 0, 0) + βDX I| O 0 (0, 0, 0, 0, 0) has the characteristic polynomial (t 2 + β 2 ) 2 , which has non-distinct eigenvalues. Its stability property can be established using an algebraic method (see [1], [5], [6], [7]). More precisely, the system of algebraic equations H(x 1 , y 1 , x 2 , y 2 , z) = H(0, 0, 0, 0, 0), I(x 1 , y 1 , x 2 , y 2 , z) = I(0, 0, 0, 0, 0), C(x 1 , y 1 , x 2 , y 2 , z) = C(0, 0, 0, 0, 0) has as unique solution the equilibrium (0, 0, 0, 0, 0), leading to the following stability result.…”