: lemmas or lemmata) is a generally minor, proven proposition which is used to prove a larger statement.
[5] From the Ancient Greek λῆμμα, (perfect passive εἴλημμαι) something received or taken.
However, a lemma can be considered a minor result whose sole purpose is to help prove a more substantial theorem – a step in the direction of proof.
[5] Some powerful results in mathematics are known as lemmas, first named for their originally minor purpose.
These include, among others: While these results originally seemed too simple or too technical to warrant independent interest, they have eventually turned out to be central to the theories in which they occur.