Linguistic Premise
Premise of Algebraic Linguistics 4-1
TANAKA Akio
1 <presheaf>
Topological space X
Open set of X U
Abelian group F ( U ) assumption F ( 0 ) = { 0 }
Element of F ( U ) Section in F over U
Map between sets U → U ’
Restriction map Homomorphism rUU’ F : F ( U ’ ) → F ( U ) assumption rUU F = id F ( U ) and rUU’ ◯ rU’U’ ‘= rUU’’
Presheaf is contrafunctor from category of open set over X to category of abelian group.
Contrafunctor and category are the terms of category theory. The definitions are omitted now.
2 <sheaf>
Topological space X
Open set of X U
Union among finite or infinite open sets U = ∪λ∈ΛUλ
Uλμ := Uλ∩Uμ
F ( U ) = Ker [ Пλ, μ∈Λ : Пλ∈ΛF ( Uλ ) → Пλ, μ∈ΛF ( Uλμ ) ]
Ker is kernel. Refer to
The upper formula expressed function’s globalization and localized functions’ putted globalized situation.
3 <structure sheaf>
Topological space X
Open set of X U
Topological manifold M
Real number valued continuous functions over U Г( U, O M )
O M is structure sheaf that defines geometric structure. One of the generalized structures is scheme.
4 <stalk and germ>
Topological space X
Open set of X U
Abelian group F ( U ) assumption F ( 0 ) = { 0 }
Point P ∈ X
Neighborhood of the point { U ; P ∈ U }
Stalk of presheaf at P direct limit Fp = lim P ∈ U F ( U )
Element of stalk Fp Germ of presheaf at P
5 <homomorphism of presheaf>
Presheaf F , G
Open set U
Homomorphism f ( U ) : F ( U ) → G ( U )
assumption rUU’ F : F ( U ’ ) → F ( U ) F ( U ) ◯ rUU’ F = rUU’ G ◯ F ( U ’ )
F ( U ) is subsheaf of G , when f ( U ) is surjection of subset.
6 <kernel of sheaf>
Sheaf F , G
Open set U
Homomorphism f ( U ) : F ( U ) → G ( U )
K is subsheaf of F , when K ( U ) = Ker ( f ( U ) ) .
K is kernel ,expressed by Ker ( f ).
7 <quotient sheaf>
Presheaf G ⊂ F
Quotient sheaf F / G is associated from presheaf F ( U ) / G ( U ).
Tokyo September 29, 2007
Sekinan Research Field of Language
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