Complex sentence: In mathematics, a "helping theorem" or lemma (plural lemmata or lemmas) is a proved proposition which is used as a stepping stone to a larger result rather than as a statement of interest by itself.
Split into simpler sentences: In mathematics, a lemma (plural lemmata or lemmas) is a proven statement used for proving another statement. It is used as a stepping stone to a larger result rather than as a statement of interest by itself.