“…As Sontag et al pointed out in [15, p. 297], checking this condition in practice is often not so easy, or even worse: a system may be monotone but fail to satisfy the stronger notion (see, e.g., [5,15,16,25] and many references therein). The second author has introduced an integer-valued function to get rid of the irreducibility condition and proved the global convergence for various monotone systems, for example, systems for every equilibrium being stable [9], sublinearity [10], systems possessing a first integral with positive gradient [11]; this technique has even been applied to the study of skew-product monotone systems without stronger notion (see [14] and [17]). This idea was first formed by the second author in [12] to solve a global stability conjecture for three dimensional cooperative systems without irreducibility.…”