On the (1, 3) distributions of limit cycles of plane quadratic systems

In this paper, (a) we revise Theorem 2 of Ref. 1] omit the condition : (b) we discuss the relative positions of six curvesM(s ², r)=0, J(s², r)=0, L(s², r)=0, T(s², r)=0, s²=s ₊ ² ands ²=s ₋ ² . Under the condition of the (1.3) distributions of limit cycles, we expand the variable regions of parameters (s, r) and clearly show them in figure; (c) we study the (1,3) distributions of limit cycles of one kind quadratic systems with two singular points at the infinite; and (d) we give a general method to discuss the (1,3) distibutions of limit cycles of system (1.1) whatever there is one, two or three singular points at the infinite