Lawrence M. Perko

Bifurcation of Limit Cycles from Centers and Separatrix Cycles of Planar Analytic Systems

T. R. Blows, Lawrence M. Perko, L. Perko, 1994, SIAM Rev..

Higher order averaging and related methods for perturbed periodic and quasi-periodic systems

Lawrence M. Perko, L. Perko, 1969 .