[marmight]

In general, an idempotent method is a method such that calling it one time is the same as calling it n times in a row for any n > 1. However, idempotency doesn't require that calling the method one time is the same as calling it zero times, although such a method isn't excluded from the definition either. So a stateless method is necessarily idempotent, but an idempotent method isn't necessarily stateless.