The Heisenberg group is with the non-commutative group law . This group law commutes with the dilation , so cannot have a Riemannian metric on it. Instead, it is equipped with a sub-Riemannian metric: an inner product on a distribution over . At the origin, this distribution gives the XY plane, and the inner product is just the Euclidean inner product on this two-dimensional subspace. This horizontal distribution and inner product is defined at the other points using invariance under left multiplication. Here is the standard picture of the horizontal distribution. We just show what happens along the XY plane. Vertical translation by acts as the identity on the distribution.