From firstname.lastname@example.org@21:1/5 to All on Fri Sep 4 05:00:25 2015
On Wednesday, December 17, 2014 at 10:58:10 AM UTC-6, Alexey Popov
However the main question remains:
Why an external differential exists in multiple different situations?
The key underlying structures and concepts are: Natural Bundles,
Natural Operations and Natural Objects. I've not seen a good or simple definition of any of these things until just now ... http://ncatlab.org/nlab/show/natural+bundle
The "definition" I've been going on up to now is that a natural object
is whatever you can do a Lie Derivative on (so technically this
statement is a conjecture of mine though probably a well-known result).