Poincaré's Lemma

Let $\wedge$ denote the Wedge Product and $D$ the Exterior Derivative. Then

$$D^2t = {\partial\over\partial x}\wedge \left({{\partial\over... ...\partial x}\wedge {\partial\over\partial x}}\right)\wedge t=0.$$

See also Differential Form, Exterior Derivative, Poincaré's Holomorphic Lemma, Wedge Product