Noether symmetries and critical exponents. Bozhkov, Yuri (2005) SIGMA. Symmetry, Integrability and Geometry: Methods and Applications [electronic only]
Nonlinear dynamical systems and KCC-theory. Yajima, Takahiro, Nagahama, Hiroyuki (2008) Acta Mathematica Academiae Paedagogicae Nyí regyháziensis. New Series [electronic only]