nLab jet comonad



Differential geometry

synthetic differential geometry


from point-set topology to differentiable manifolds

geometry of physics: coordinate systems, smooth spaces, manifolds, smooth homotopy types, supergeometry



smooth space


The magic algebraic facts




infinitesimal cohesion

tangent cohesion

differential cohesion

graded differential cohesion

singular cohesion

id id fermionic bosonic bosonic Rh rheonomic reduced infinitesimal infinitesimal & étale cohesive ʃ discrete discrete continuous * \array{ && id &\dashv& id \\ && \vee && \vee \\ &\stackrel{fermionic}{}& \rightrightarrows &\dashv& \rightsquigarrow & \stackrel{bosonic}{} \\ && \bot && \bot \\ &\stackrel{bosonic}{} & \rightsquigarrow &\dashv& \mathrm{R}\!\!\mathrm{h} & \stackrel{rheonomic}{} \\ && \vee && \vee \\ &\stackrel{reduced}{} & \Re &\dashv& \Im & \stackrel{infinitesimal}{} \\ && \bot && \bot \\ &\stackrel{infinitesimal}{}& \Im &\dashv& \& & \stackrel{\text{étale}}{} \\ && \vee && \vee \\ &\stackrel{cohesive}{}& \esh &\dashv& \flat & \stackrel{discrete}{} \\ && \bot && \bot \\ &\stackrel{discrete}{}& \flat &\dashv& \sharp & \stackrel{continuous}{} \\ && \vee && \vee \\ && \emptyset &\dashv& \ast }


Lie theory, ∞-Lie theory

differential equations, variational calculus

Chern-Weil theory, ∞-Chern-Weil theory

Cartan geometry (super, higher)

Category theory




In a context H\mathbf{H} of differential cohesion with \Im the infinitesimal shape modality, then for any object XHX\in \mathbf{H} the base change comonad

Jet Xi *i * Jet_X \coloneqq i^\ast i_\ast

for base change along the XX-component of the unit of \Im

H /Xi *i *H /(X), \mathbf{H}_{/X} \stackrel{\overset{i^\ast}{\longleftarrow}}{\underset{i_\ast}{\longrightarrow}} \mathbf{H}_{/\Im(X)} \,,

may be interpreted as sending any bundle over XX to its jet bundle.

This characterization via base change is more or less implicit in (Kock 10, remark 7.3.1) (to translate from the pull-push (p 2) *p 1 *(p_2)_\ast p_1^\ast shown there, as in (Deligne 70) use that in a topos the epimorphism XXX \to \Im X is effective and then use the Beck-Chevalley condition to get the push-pull shown above.)

{T X p 1 X p 2 (pb) i X X i X X}((p 2) *(p 1) *(i X) *(i X) *). \left\{ \array{ T^\infty X &\stackrel{p_1}{\longrightarrow}& X \\ \downarrow^{\mathrlap{p_2}} &(pb)& \downarrow^{\mathrlap{i_X}} \\ X &\stackrel{i_X}{\longrightarrow}& \Im X } \right\} \;\; \Rightarrow \;\; ((p_2)_\ast (p_1)^\ast \simeq (i_X)^\ast (i_X)_\ast) \,.

T XT^\infty X is the infinitesimal disk bundle.


The Eilenberg-Moore category of coalgebras over the jet comonad has the interpretation of the category of partial differential equations with variables in XX. The co-Kleisli category of the jet comonad has the interpretation as being the category of bundles over XX with differential operators between them as morphisms (Marvan 86, Marvan 89).


In the context of differential geometry the comonad structure on the jet bundle construction, as well as the interpretation of its EM-category as that of partial differential equations, is due to

  • Michal Marvan, A note on the category of partial differential equations, in Differential geometry and its applications, Proceedings of the Conference August 24-30, 1986, Brno (pdf)

(Proposition 1.4 in Marvan 86 needs an extra “weakened transversality” condition on the equalizer, this is fixed in (Theorem 1.3, Marvan’s thesis). The extra condition is that the equalizer must remain an equalizer after an application of the VV functor, which maps fibered manifolds to their vertical tangent bundles.)

Discussion in synthetic differential geometry:

  • Pierre Deligne, Equations Différentielles à Points Singuliers Réguliers, 1970

  • Anders Kock, remark 7.3.1 Synthetic geometry of manifolds, Cambridge Tracts in Mathematics 180 (2010). (pdf)

In the context of algebraic geometry and D-geometry the comonad structure is observed in:

  • Jacob Lurie, Notes on crystals and algebraic 𝒟\mathcal{D}-modules (2010) [pdf]

Discussion in differential cohesion:

Discussion in differentially cohesive modal homotopy type theory:

For more references see at jet bundle.

Last revised on May 4, 2023 at 12:08:02. See the history of this page for a list of all contributions to it.