nLab theory of abelian groups

Contents

Context

Type theory

Topos Theory

natural deduction metalanguage, practical foundations

  1. type formation rule
  2. term introduction rule
  3. term elimination rule
  4. computation rule

type theory (dependent, intensional, observational type theory, homotopy type theory)

syntax object language

computational trinitarianism =
propositions as types +programs as proofs +relation type theory/category theory

logicset theory (internal logic of)category theorytype theory
propositionsetobjecttype
predicatefamily of setsdisplay morphismdependent type
proofelementgeneralized elementterm/program
cut rulecomposition of classifying morphisms / pullback of display mapssubstitution
introduction rule for implicationcounit for hom-tensor adjunctionlambda
elimination rule for implicationunit for hom-tensor adjunctionapplication
cut elimination for implicationone of the zigzag identities for hom-tensor adjunctionbeta reduction
identity elimination for implicationthe other zigzag identity for hom-tensor adjunctioneta conversion
truesingletonterminal object/(-2)-truncated objecth-level 0-type/unit type
falseempty setinitial objectempty type
proposition, truth valuesubsingletonsubterminal object/(-1)-truncated objecth-proposition, mere proposition
logical conjunctioncartesian productproductproduct type
disjunctiondisjoint union (support of)coproduct ((-1)-truncation of)sum type (bracket type of)
implicationfunction set (into subsingleton)internal hom (into subterminal object)function type (into h-proposition)
negationfunction set into empty setinternal hom into initial objectfunction type into empty type
universal quantificationindexed cartesian product (of family of subsingletons)dependent product (of family of subterminal objects)dependent product type (of family of h-propositions)
existential quantificationindexed disjoint union (support of)dependent sum ((-1)-truncation of)dependent sum type (bracket type of)
logical equivalencebijection setobject of isomorphismsequivalence type
support setsupport object/(-1)-truncationpropositional truncation/bracket type
n-image of morphism into terminal object/n-truncationn-truncation modality
equalitydiagonal function/diagonal subset/diagonal relationpath space objectidentity type/path type
completely presented setsetdiscrete object/0-truncated objecth-level 2-type/set/h-set
setset with equivalence relationinternal 0-groupoidBishop set/setoid with its pseudo-equivalence relation an actual equivalence relation
equivalence class/quotient setquotientquotient type
inductioncolimitinductive type, W-type, M-type
higher inductionhigher colimithigher inductive type
-0-truncated higher colimitquotient inductive type
coinductionlimitcoinductive type
presettype without identity types
set of truth valuessubobject classifiertype of propositions
domain of discourseuniverseobject classifiertype universe
modalityclosure operator, (idempotent) monadmodal type theory, monad (in computer science)
linear logic(symmetric, closed) monoidal categorylinear type theory/quantum computation
proof netstring diagramquantum circuit
(absence of) contraction rule(absence of) diagonalno-cloning theorem
synthetic mathematicsdomain specific embedded programming language

homotopy levels

semantics

topos theory

Background

Toposes

Internal Logic

Topos morphisms

Extra stuff, structure, properties

Cohomology and homotopy

In higher category theory

Theorems

Contents

Idea

The theory of abelian groups TT is the logical theory whose models in a cartesian category are the abelian group objects.

Definition

The theory of abelian groups TT is the theory over the signature with one sort XX, one constant 00, two function symbols ++ (of sort X×XXX\times X\to X) and - (of sort XXX\to X) and equality with axioms:

  • xx+0=x\top\vdash_x x+0=x \quad
  • x,y,zx+(y+z)=(x+y)+z\top\vdash_{x,y,z} x+(y+z)=(x+y)+z\quad,
  • xx+(x)=0\top\vdash_x x+(-x)=0\quad.
  • x,yx+y=y+x\top\vdash_{x,y} x+y=y+x\quad.

The theory of abelian groups is algebraic. In the following we list some extensions that use increasingly stronger fragments of geometric logic.

Extensions of the theory of abelian groups

The theory of torsion-free abelian groups T T^\infty results from TT by addition of the following axioms:

  • For all n2n\geq 2: ((nx=0)) x(x=0))((nx=0))\vdash_x (x=0))\quad.

The resulting theory is a Horn theory.

The theory of divisible abelian groups T \T^\backslash results from TT by addition of the following regular axioms:

  • For all n2n\geq 2: x(y)(ny=x)\top\vdash_x (\exists y) (ny=x)\quad.

The theory of divisible torsion-free abelian groups T \T^{\backslash\infty} results from T \T^\backslash by adding the above axioms for torsion-freeness. The resulting theory is cartesian.

The theory of torsion abelian groups T ~T^~ is an infinitary geometric theory resulting from TT by addition of:

  • x n2(nx=0)\top\vdash_x \bigvee_{n\geq 2} (nx=0)\quad.

References

Last revised on October 29, 2014 at 12:58:28. See the history of this page for a list of all contributions to it.