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unusual facts about Schanuel's lemma


Schanuel's lemma

In mathematics, especially in the area of algebra known as module theory, Schanuel's lemma, named after Stephen Schanuel, allows one to compare how far modules depart from being projective.


Aronszajn tree

The existence of Aronszajn trees (=\aleph 1-Aronszajn trees) was proven by Nachman Aronszajn, and implies that the analogue of König's lemma does not hold for uncountable trees.

Burnside's lemma

Consequently, this lemma is sometimes referred to as the lemma that is not Burnside's.

Hensel's lemma

Masayoshi Nagata proved in the 1950s that for any commutative local ring A with maximal ideal m there always exists a smallest ring Ah containing A such that Ah is Henselian with respect to mAh.

Completeness of a ring is not a necessary condition for the ring to have the Henselian property: Goro Azumaya in 1950 defined a commutative local ring satisfying the Henselian property for the maximal ideal m to be a Henselian ring.

Hotelling

Hotelling's lemma: an economic rule relating the supply of a good to the profit of the good's producer

König's theorem

König's lemma (also known as König's infinity lemma), named after Dénes Kőnig

Oka's lemma

In mathematics, Oka's lemma, proved by Kiyoshi Oka, states that in a domain of holomorphy in Cn, the function –log d(z) is plurisubharmonic, where d is the distance to the boundary.

Quillen's lemma

In contrast to a version of Schur's lemma due to Dixmier, it does not require k to be uncountable.

Scheffé’s lemma

Henry Scheffé published a proof of the statement on convergence of probability densities in 1947.

Shephard's lemma

The lemma is named after Ronald Shephard who gave a proof using the distance formula in his book Theory of Cost and Production Functions (Princeton University Press, 1953).

Transcendence theory

Stephen Schanuel conjectured that the answer is n, but no proof is known.

Zorn's Law

Zorn's lemma is a proposition used in many areas of theoretical mathematics.

Zorn's lemma

# Banach's extension theorem which is used to prove one of the most fundamental results in functional analysis, the Hahn–Banach theorem

It occurs in the proofs of several theorems of crucial importance, for instance the Hahn–Banach theorem in functional analysis, the theorem that every vector space has a basis, Tychonoff's theorem in topology stating that every product of compact spaces is compact, and the theorems in abstract algebra that every nonzero ring has a maximal ideal and that every field has an algebraic closure.


see also