nLab finite homotopy type



Homotopy theory

homotopy theory, (∞,1)-category theory, homotopy type theory

flavors: stable, equivariant, rational, p-adic, proper, geometric, cohesive, directed

models: topological, simplicial, localic, …

see also algebraic topology



Paths and cylinders

Homotopy groups

Basic facts


Type 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

logiccategory theorytype theory
trueterminal object/(-2)-truncated objecth-level 0-type/unit type
falseinitial objectempty type
proposition(-1)-truncated objecth-proposition, mere proposition
proofgeneralized elementprogram
cut rulecomposition of classifying morphisms / pullback of display mapssubstitution
cut elimination for implicationcounit for hom-tensor adjunctionbeta reduction
introduction rule for implicationunit for hom-tensor adjunctioneta conversion
logical conjunctionproductproduct type
disjunctioncoproduct ((-1)-truncation of)sum type (bracket type of)
implicationinternal homfunction type
negationinternal hom into initial objectfunction type into empty type
universal quantificationdependent productdependent product type
existential quantificationdependent sum ((-1)-truncation of)dependent sum type (bracket type of)
equivalencepath space objectidentity type/path type
equivalence classquotientquotient type
inductioncolimitinductive type, W-type, M-type
higher inductionhigher colimithigher inductive type
-0-truncated higher colimitquotient inductive type
coinductionlimitcoinductive type
presettype without identity types
completely presented setdiscrete object/0-truncated objecth-level 2-type/set/h-set
setinternal 0-groupoidBishop set/setoid
universeobject classifiertype of types
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





A homotopy type is called finite if it is presented (via the discussion at homotopy hypothesis) by either


Similarly a spectrum (stable homotopy type) given by a sequence of finite homotopy types is called a finite spectrum.


Beware that a finite homotopy type in general does not have finite and finitely many homotopy groups (see e.g. at homotopy groups of spheres). Homotopy types with finite and finitely many homotopy groups have alternatively been called π\pi-finite, or tame, or (adapted from homological algebra) “of finite type” (which needs to be carefully distinguishes, therefore, from “finite homotopy type”). See at homotopy type with finite homotopy groups.


Relation to compact homotopy type

The compact objects in ∞Grpd are the retracts of finite homotopy types. Not every such retract is itself a finite homotopy type; the vanishing of Wall's finiteness obstruction is a necessary and sufficient condition for this to happen.


Last revised on July 8, 2021 at 15:36:43. See the history of this page for a list of all contributions to it.