In the theory of formal languages in computability theory, a pumping lemma or pumping argument states that, for a particular language to be a member of a language class, any sufficiently long string in the language contains a section, or sections, that can be removed, or repeated any number of times, with the resulting string remaining in that language. The proofs of these lemmas typically require counting arguments such as the pigeonhole principle.
The two most important examples are the pumping lemma for regular languages and the pumping lemma for context-free languages. Ogden's lemma is a second, stronger pumping lemma for context-free languages.
These lemmas can be used to determine if a particular language is not in a given language class. However, they cannot be used to determine if a language is in a given class, since satisfying the pumping lemma is a necessary, but not sufficient, condition for class membership.
Famous quotes containing the word pumping:
“It is by teaching that we teach ourselves, by relating that we observe, by affirming that we examine, by showing that we look, by writing that we think, by pumping that we draw water into the well.”
—Henri-Frédéric Amiel (1821–1881)