Fundamental_lemma_of_sieve_theory
In number theory, the fundamental lemma of sieve theory is any of several results that systematize the process of applying sieve methods to particular problems. Halberstam & Richert [1]: 92–93 write:
A curious feature of sieve literature is that while there is frequent use of Brun's method there are only a few attempts to formulate a general Brun theorem (such as Theorem 2.1); as a result there are surprisingly many papers which repeat in considerable detail the steps of Brun's argument.
Diamond & Halberstam[2]: 42 attribute the terminology Fundamental Lemma to Jonas Kubilius.