In this paper, the rule for the lengths of positive and negative semicycles of nontrivial solutions of the following fourth-order rational difference equation,xn+1=xnbxn-2+xn-3b+axnb+xn-2xn-3b+a,n=0,1,2,..., where a, b ε [0, ∞) and the initial values x-3,x-2,x -1,x0 ε (0, ∞), to successively occur is found to be ..., 4+, 3-, 1+, 2-, 2 +, 1-, 1+, 1-, 4+, 3 -, 1+, 2-, 2+, 1-, 1 +, 1-, 4+, 3-, 1+, 2 -, 2+, 1-, 1+, 1-, ..., by which the positive equilibrium point of the equation is verified to be globally asympto...