The convention is this: we use e.g. nat.is_inhabited and nat.has_decidable_eq
for these two purposes only, to avoid clashing with "inhabited" and "decidable_eq"
in a namespace. Otherwise, we use "decidable_foo" and "inhabited_foo".
also add more definitions in types.pi, types.path, algebra.precategory
the (pre)category library still needs cleanup
authors of this commit: @avigad, @javra, @fpvandoorn
The new command provides a uniform way to set declaration attributes.
It replaces the commands: class, instance, coercion, multiple_instances,
reducible, irreducible
