[1] R. W. Brockett, J. L. Willems: Frequency domain stability criteria. Part I and II. IEEE Trans. Automat. Control AC-10 (1965), 3, 4, 255-261, 401-413. MR 0186423

[2] C. A. Desoer, Y. T. Wang: The robust nonlinear servomechanism problem. Internat. J. Control 20 (1979), 5, 803-828. MR 0535671 | Zbl 0429.93021

[3] C A. Desoer, C A. Lin: Tracking and disturbance rejection of MIMO nonlinear systems with PI controller. IEEE Trans. Automat. Control AC-30 (1985), 9, 861-867. MR 0799479 | Zbl 0573.93027

[4] B. Francis: The linear multivariable regulator problem. SI AM J. Control Optim. 15 (1977), 486--505. MR 0446631

[5] B. Francis, W. M. Wonham: The internal model principle for linear multivariable regulators. Appl. Math. Optim. 2 (1975), 2, 170-194. MR 0389331 | Zbl 0351.93015

[6] P. Molander, J. C Willems: Synthesis of state feedback control laws with a specified gain and phase margin. IEEE Trans. Automat. Control AC-25 (1980), 5, 928-931. MR 0595228 | Zbl 0461.93046

[7] V. M. Popov: On a critical case of absolute stability. Avtomat. i Telemekh. 23 (1962), 2, 3 - 24. In Russian. MR 0159998

[8] V. M. Popov: Hyperstability of Control Systems. Springer-Verlag, Berlin-Heidelberg- New York 1973. MR 0387749 | Zbl 0276.93033

[9] B. Porter, Lj. Grujić: Tracking systems incorporating Lur'e type plants. Internát. J. Systems Sci. 11 (1980), 12, 1505-1520. MR 0601677

[10] W. M. Wonham: Linear Multivariable Control: A Geometric Approach. Springer-Verlag, Berlin-Heidelberg-New York 1979. MR 0569358 | Zbl 0424.93001