holds for all cotangent vectors p in T q ∗ Q {\displaystyle T_{q}^{*}Q} . Here, X q {\displaystyle X_{q}} is a vector in T q Q {\displaystyle T_{q}Q} , the tangent space to the manifold Q at point q. The function P X {\displaystyle P_{X}} is called the momentum function corresponding to X.