1. Agashe SD (1967) Some generalizations in system theory and their applications to control systems”, Ph.D. Thesis, Coordinated Science Laboratory, University of Illinois -Urbana, Report R-356
2. Boltianskii VG (1958) The maximum principle in the theory of optimal processes”, Reports of the Academy of Sciences, USSR, 119(6): 1079–1073, USSR
3. Boltianskii VG, Gamkrelidze RV and Pontryagin LS (1956) Toward the theory of optimal processes, Report of the Academy of Sciences USSR, 11(1): 7-10
4. Brandt-Pollmann U et al (2008) Numerical solution of optimal control problems with constant control dealys. Comput Econ 31:181–206
5. Butkovaskii AG (1961a) Optimal processes in distributed parameter systems. Autom Remote Control 22(1):17–26