Projectable vector field

Classical setup

Consider a map f:MN. We say that a vector field XX(M) projects on YX(N) if they are f-related vector fields. We will say that XX(M) is projectable if it projects to some vector field on N. See @saunders1989geometry page 67.

By the way, if f is a smooth submersion, giving a vector field YX(N) there is at least one projectable vector field X which is f-related to Y. See this answer in math.stackexchange

Along distributions

Given an involutive distribution X (i.e., a foliation) on a manifold M, a vector field Y is said to be projectable with respect to X (in the sense of @paola.frobenius) if for every XΓ(M,X) we have

[Y,X]Γ(M,X)

They are also known as foliate vector fields, basic vector fields, base-like vector fields, foliated vector fields,... (see [Molino 1988] page 35)

In particular, it may happen that X=S({X}), and the requirement becomes

[Y,X]=ρX

We can say that Y is a X-projectable vector field.

But, what is happening when we reduce an ODE with a symmetry? I.e., when we have a vector field A associated to an ODE and

[A,X]=ξA

The point here is that the vector field is not X-projectable, but the distribution {A} is. The projection converts the vector field A in a nonlocal vector field!?
But we would have had the same phenomenon if [A,X]=ξA+ρX, i.e., if X were a cinf-symmetry.

This open the door to: a distribution A=S({A1,A2}) is X-projectable if S({A1,A2,X}) is involutive, that is, X is a cinf-symmetry of distribution A.