Re: The momentum - a cotangent vector?

I think Stefan is using "tangent vector" and "cotangent vector"
in the sense of differential geometry and tensor calculus.  In
this usage, these phrases describe how a vector (a.k.a a rank-1
tensor) transforms under a change of coordintes: a tangent vector
(a.k.a a "contravariant vector") is a vector which transforms the
same way a coordinate position $x^i$ does, while a cotangent vector
(a.k.a a "covariant vector") is a vector which transforms the same
way a partial derivative operator $\partial / \partial x^i$ does.