If the part of the real axis between two o.l.poles (o.l.zeros) belongs to the loci, there must be a point of breakaway form, or arrival at, the real axis.

• 如果实轴的一部分位于两个开环极点（或者开环零点）之间且属于轨迹，则在其间必有分离点（或者会合点）。