This theory has been considered by many mathematicians starting with Poincare, Liapunov and Birkhoff. It was then that Smale enriched the theory substantially by defining as a main objective the search for generic and stable properties and by obtaining results and proposing problems of great relevance in this context.
Subnormal Subgroups of Groups by John C. Lennox & Stewart E. Stonehewer 1987 HC
It covers the subject areas of science, mathematics, and group theory, making it a valuable resource for students and researchers in these fields.