In mathematics, the Leray–Schauder degree is an extension of the degree of a

base point In mathematics, a pointed space or based space is a topological space with a distinguished point, the basepoint. The distinguished point is just simply one particular point, picked out from the space, and given a name, such as x_0, that remains u ...

preserving

continuous map In mathematics, a continuous function is a function such that a continuous variation (that is a change without jump) of the argument induces a continuous variation of the value of the function. This means that there are no abrupt changes in va ...

between

sphere A sphere () is a Geometry, geometrical object that is a solid geometry, three-dimensional analogue to a two-dimensional circle. A sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...

(S^n, *) \to (S^n , *)

or equivalently to a boundary sphere preserving continuous maps between balls

(B^n, S^) \to (B^n, S^)

to boundary sphere preserving maps between balls in a

Banach space In mathematics, more specifically in functional analysis, a Banach space (pronounced ) is a complete normed vector space. Thus, a Banach space is a vector space with a metric that allows the computation of vector length and distance between ve ...

f: (B(V), S(V)) \to (B(V), S(V))

, assuming that the map is of the form

f = id - C

where

id

is the

identity map Graph of the identity function on the real numbers In mathematics, an identity function, also called an identity relation, identity map or identity transformation, is a function that always returns the value that was used as its argument, un ...

and

C

is some compact map (i.e. mapping bounded sets to sets whose closure is

compact Compact as used in politics may refer broadly to a pact or treaty; in more specific cases it may refer to: * Interstate compact * Blood compact, an ancient ritual of the Philippines * Compact government, a type of colonial rule utilized in British ...

). The degree was invented by

Jean Leray Jean Leray (; 7 November 1906 – 10 November 1998) was a French mathematician, who worked on both partial differential equations and algebraic topology. Life and career He was born in Chantenay-sur-Loire (today part of Nantes). He studied at Éc ...

and

Juliusz Schauder Juliusz Paweł Schauder (; 21 September 1899, Lwów, Austria-Hungary – September 1943, Lwów, Occupied Poland) was a Polish mathematician of Jewish origin, known for his work in functional analysis, partial differential equations and m ...

to prove existence results for partial differential equations.Mawhin, J. (2018). A tribute to Juliusz Schauder. '' Antiquitates Mathematicae'', ''12''.

References

Topology {{DEFAULTSORT:Leray-Schauder degree