Nonclassical approximate symmetries of evolution equations with a small parameter. Kordyukova, Svetlana (2006) SIGMA. Symmetry, Integrability and Geometry: Methods and Applications [electronic only]
Nonlocal symmetries and generation of solutions for partial differential equations. Tychynin, Valentyn, Petrova, Olga, Tertyshnyk, Olesya (2007) SIGMA. Symmetry, Integrability and Geometry: Methods and Applications [electronic only]