Method change_index() added for changing index.
Example failures fixed.
Example failures fixed.
Example failures fixed.
Example failures fixed.
polys: Use __nonzero__ instead of __bool__ and let 2to3 do its job
polys: Don't use __slots__ in GroebnerBasis
Start the intro for the new tutorial
Should be \cdot, not \dot
Fix doctests
Get rid of (apparently unnecessary) ::
Finish up the intro
Allow to specify the generators when building monomial_key.

This allows to obtain a sort key that can be directly applied
to sort Expr instances; it casts Expr into Poly with the given
generators and then applies the chosen ordering.
change_index() updated. Doctests fixed.
Address Sean's comments
change_index() updated. Doctests fixed.
Add a gotchas file to the new tutorial
Start work on preliminaries and simplification files for the new tutorial
Write some more of the simplification document
Add polynomial simplification stuff to the new tutorial