I'm reading a book on quontum mechanics in japanese (Quontum Mechanics by Shinichiro Tomonaga) and am stuck in proving the action variable "J" is constant in a one dimentional cyclic movement. i.e. The action variable "J" created by the trajectory of H(p(t),q(t),a(t/T)) = E(t) doesn't change. This trajectory won't make a closed region when a(t/T) changes, but when a(t/T) is fixed or changes very slowly the trajectory is assumed to be closed. Will anyone give me good online references on it, or recommend nice English books on Quontum Mechanics (not so thick or thin) ? Japanese books don't look nice to me. I'm good at math and have knowledge on electromagnetic mechanics and special/general theories of relativity, but not quontum mechanics. Thanks in advance!