Structure 1-form of a distribution D

Let D be a distribution on M, and V~=TM/D. We have a canonical map (it looks like a projection)

θ:TMV~θ(v):=v mod D

Observe that θΩ1(M,V~)=Ω1(M)Γ(V~), and it is called structure 1-form of D.

In other words, is the projection over, in some sense, the vertical bundle. When D is a connection on a fiber bundle (if M has itself an internal bundle structure), we have a well defined projection of TpM on a vertical subspace, and the structure 1-form corresponds to the connection 1-form.

This is related to the dual description of the distribution, since in a local chart θ can be seen as nk forms such that their annihilator describe D.