Also, give names to hypotheses that we refer to.

Also add "Local" to some Default Proof Using to keep them more contained

This approach is originally by Robbert

This patch was created using

  find -name *.v | xargs -L 1 awk -i inplace '{from = 0} /^From/{ from = 1; ever_from = 1} { if (from == 0 && seen == 0 && ever_from == 1) { print "Set Default Proof Using \"Type*\"."; seen = 1 } }1 '

and some minor manual editing

I added the old one in 176a588c but it was never used.

Using this new definition we can express being contractive using a
Proper. This has the following advantages:

- It makes it easier to state that a function with multiple arguments
  is contractive (in all or some arguments).
- A solve_contractive tactic can be implemented by extending the
  solve_proper tactic.

This removes Ralf's hack of using later_car, which is not function in the logic.

Thanks to Aleš for suggesting this.