Fix typo in index in the definition of the Jacobian.

Mark John Hopkins

]]>“a tangent bundle” → “the tangent bundle”, plus fixing typo.

Mark John Hopkins

]]>I have added to *vielbein* a far bit of discussion of vielbein fields as witnesses of reduction of the structure group of the tangent bundle.

I have added to *vielbein* a discussion of the vielbein as an orthogonal structure and, more in details as an example of a tiwsted differential c-structure for $\mathbf{c} : \mathbf{B} O(n) \to \mathbf{B} GL(n)$.