extension lemma
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HNN extension — In mathematics, the HNN extension is a basic construction of combinatorial group theory.Introduced in a 1949 paper Embedding Theorems for Groups [ cite journal|title=Embedding Theorems for Groups|journal=Jornal of the London Mathematical… … Wikipedia
Massera's lemma — In stability theory and nonlinear control, Massera s lemma, named after José Luis Massera, deals with the construction of the Lyapunov function to prove the stability of a dynamical system.[1] The lemma appears in (Massera 1949, p. 716) as… … Wikipedia
Ping-pong lemma — In mathematics, the ping pong lemma, or table tennis lemma, is any of several mathematical statements which ensure that several elements in a group acting on a set freely generate a free subgroup of that group.HistoryThe ping pong argument goes… … Wikipedia
Nakayama lemma — In mathematics, more specifically modern algebra and commutative algebra, Nakayama s lemma also known as the Krull–Azumaya theorem[1] governs the interaction between the Jacobson radical of a ring (typically a commutative ring) and its finitely… … Wikipedia
König's lemma — or König s infinity lemma is a theorem in graph theory due to Dénes Kőnig (1936). It gives a sufficient condition for an infinite graph to have an infinitely long path. The computability aspects of this theorem have been thoroughly investigated… … Wikipedia
Fatou's lemma — In mathematics, Fatou s lemma establishes an inequality relating the integral (in the sense of Lebesgue) of the limit inferior of a sequence of functions to the limit inferior of integrals of these functions. The lemma is named after the French… … Wikipedia
Yoneda lemma — In mathematics, specifically in category theory, the Yoneda lemma is an abstract result on functors of the type morphisms into a fixed object . It is a vast generalisation of Cayley s theorem from group theory (a group being a particular kind of… … Wikipedia
Abhyankar's lemma — In mathematics, Abhyankar s lemma (named after Shreeram Shankar Abhyankar) allows one to kill tame ramification by taking an extension of a base field. More precisely, Abhyankar s lemma states that if A , B , C are local fields such that A and B… … Wikipedia
Schwarz lemma — In mathematics, the Schwarz lemma, named after Hermann Amandus Schwarz, is a result in complex analysis about holomorphic functions defined on the open unit disk. Lemma statementLet D = {z : |z| < 1} be the open unit disk in the complex plane C.… … Wikipedia
Ogden's lemma — In the theory of formal languages, Ogden s lemma (named after William F. Ogden) provides an extension of flexibility over the pumping lemma for context free languages. Ogden s lemma states that if a language L is context free, then there exists… … Wikipedia
Urysohn's lemma — In topology, Urysohn s lemma, sometimes called the first non trivial fact of point set topology , is commonly used to construct continuous functions of various properties on normal spaces. It is widely applicable since all metric spaces and all… … Wikipedia
