[IEEE 1977 IEEE Conference on Decision and Control including the 16th Symposium on Adaptive Processes and A Special Symposium on Fuzzy Set Theory and Applications - New Orleans, LA, USA (1977.12.7-1977.12.9)] 1977 IEEE Conference on Decision and Control including the 16th Symposium on Adaptive Processes and A Special Symposium on Fuzzy Set Theory and Applications - Stability conditions for second order ordinary differential equations with periodic coefficients