1. FULLER , A. T. , 1961 ,Proc. I.F.A.C. Congress, Moscow, 1960, 1 , 510 ( London Butterworths ) .
2. Note on a Solution due to A. T. Fuller†
3. PONTRYAGIN , L. S. , 1957 ,Session of A.N.U.S.S.B, on Fundamental Problems of Automatic Controls, 2 , 107 ( Moscow A.N.U.S.S.R. ).