Lemma
 Noun
A preliminary or auxiliary proposition demonstrated or accepted for immediate use in the demonstration of some other proposition, as in mathematics or logic.
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Burnside's lemma
Burnside's lemma, sometimes also called Burnside's counting theorem, the Cauchy–Frobenius lemma

Itô's lemma
In mathematics, Itô's lemma is an identity used in Itô calculus to find the differential of a time

Kőnig's lemma
Kőnig's lemma or Kőnig's infinity lemma is a theorem in graph theory due to the Hungarian

Calderón–Zygmund lemma
In mathematics, the Calderón–Zygmund lemma is a fundamental result in Fourier analysis, harmonic

Farkas' lemma
Farkas' lemma is a solvability theorem for a finite system of linear inequalities in mathematics

Yoneda lemma
In mathematics, specifically in category theory, the Yoneda lemma is an abstract result on functors

Zorn's lemma
Zorn's lemma, also known as the Kuratowski–Zorn lemma, after mathematicians Max Zorn and Kazimierz

Five lemma
lemma can be thought of as a combination of two other theorems, the four lemmas, which are dual to each other.

Gauss's lemma
Gauss's lemma can mean any of several lemmas named after Carl Friedrich Gauss:
* Gauss's lemma

Lindström–Gessel–Viennot lemma
In mathematics, the Lindström–Gessel–Viennot lemma provides a way to count the number of tuples