Exterior Derivative question In http://mathworld.wolfram.com/ExteriorDerivative.html, 

there is a section that starts from:


  Define the exterior derivative by $Dt ≡  \frac{\partial}{\partial x} \wedge t$


First of all, what does this first part quoted mean, in relation to the previous parts?

I then want to know what the rest of the section is talking about.
The notation between the dollar sign is LaTeX (http://www.latex-project.org/) mathematics
notation. It is meant to be very descriptive of mathematical expressions; it is not intended to "look" like standard mathematical notation.

The closest equivalent in Mathematica itself is:

Dt [Congruent] ([PartialD]/[PartialD]x)[Wedge]t
The notation between the dollar sign is LaTeX (http://www.latex-project.org/) mathematics
notation. It is meant to be very descriptive of mathematical expressions; it is not intended to "look" like standard mathematical notation.

The closest equivalent in Mathematica itself is:

Dt [Congruent] ([PartialD]/[PartialD]x)[Wedge]t