In mathematics, a lemma expresses a minor theorem, of interest primarily because it serves in the proof of a major result. In a few cases, a lemma becomes well-known in its own right; this can occur when a lemma is a particularly useful restatement of another result. See Zorn's lemma and Farkas's lemma .

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In linguistics, and particularly in morphology, a lemma comprises the canonical form of a word. Lemmas have especial significance in highly inflected languages such as Czech.

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In Terry Pratchett's Discworld series, the shadowing lemma is an animal which exists in only 2 dimensions and eats mathematicians.