The exterior derivative d may be though of as a differential operator del wedge: ∇∧, where ∇=∂/∂x¹dx¹+∂/∂x_2dx²+...+∂/∂xⁿdxⁿ. Then the square of the exterior derivative is d²=∇∧∇∧=(∇∧∇)∧=0∧=0 because the wedge product is alternating. (If u is a blade and f a scalar (function), then fu≡f∧u, so d(fu)=∇∧(fu)=∇∧(f∧u)=(∇∧f)∧u=df∧u.) Another way to show that d²=0 is that partial derivatives commute and wedge products of 1-forms anti-commute (so when d² is applied to a blade then the distributed parts end up canceling to zero.)

Then he commenced to talk, really talk, and inside of two flaps of a herring’s fin he had me mesmerized, like Eben Holt’s boy at the town hall show. He talked about the ills of humanity, and the glories of health and Nature and service and land knows what all.

If this picture of the two psychical agencies and their relation to the consciousness is accepted, there is a complete analogy in political life to the extraordinary affection which I felt in my dream for my friend R., who was treated with such contumely during the dream's interpretation.

For whereof commeth thys hypocrisie in the popedome, that men shall preache free will, merits, and satisfactions, and set vp their bristles in suche wise, and beare themselues in hande that they may come perking before God, yea and preace thither lyke shamelesse strumpets.