Definition 21.8 University Mathematics — Year 3 · Chapter 21 — Differential Forms and Stokes’ Theorem The exterior derivative is the linear map d :Ωk(U)→Ωk+1(U)\dd\colon \Omega^k(U) \to \Omega^{k+1}(U)d:Ωk(U)→Ωk+1(U) defined by d(∑IaI dxI)=∑I daI∧ dxI=∑I∑j=1n∂aI∂xj dxj∧ dxI.\dd\Bigl(\sum_I a_I\,\dd x_I\Bigr) = \sum_I \dd a_I \wedge \dd x_I = \sum_I\sum_{j=1}^n \frac{\partial a_I}{\partial x_j}\,\dd x_j \wedge \dd x_I .d(I∑aIdxI)=I∑daI∧dxI=I∑j=1∑n∂xj∂aIdxj∧dxI. On 000-forms it is the usual differential. Read in context →