Section 7.1 The Feature of Integrating Systems Proof. Necessity is obvious.Consider sufficiency.Assume that the two conditions hold.It remains to show that G(s)Q(s)is stable.If G(s)Q(s)is unstable,1-G(s)Q(s)is unstable,which implies that [1-G(s)Q(s)]G(s)must be unstable.This contradicts the assumption. The conclusion may not be applicable to other structures. Consider the IMC structure shown in Figure 4口，+回，424生，定9QC Zhang.W.D..CRC Press.2011 Version 1.0 6/79Section 7.1 The Feature of Integrating Systems Proof. Necessity is obvious. Consider sufficiency. Assume that the two conditions hold. It remains to show that G(s)Q(s) is stable. If G(s)Q(s) is unstable, 1 − G(s)Q(s) is unstable, which implies that [1 − G(s)Q(s)]G(s) must be unstable. This contradicts the assumption. The conclusion may not be applicable to other structures. Consider the IMC structure shown in Figure Zhang, W.D., CRC Press, 2011 Version 1.0 6/79