This PR adjusts the experimental module system to make `private` the
default visibility modifier in `module`s, introducing `public` as a new
modifier instead. `public section` can be used to revert the default for
an entire section, though this is more intended to ease gradual adoption
of the new semantics such as in `Init` (and soon `Std`) where they
should be replaced by a future decl-by-decl re-review of visibilities.
This PR replaces `List.lt` with `List.Lex`, from Mathlib, and adds the
new `Bool` valued lexicographic comparatory function `List.lex`. This
subtly changes the definition of `<` on Lists in some situations.
`List.lt` was a weaker relation: in particular if `l₁ < l₂`, then
`a :: l₁ < b :: l₂` may hold according to `List.lt` even if `a` and `b`
are merely incomparable
(either neither `a < b` nor `b < a`), whereas according to `List.Lex`
this would require `a = b`.
When `<` is total, in the sense that `¬ · < ·` is antisymmetric, then
the two relations coincide.
Mathlib was already overriding the order instances for `List α`,
so this change should not be noticed by anyone already using Mathlib.
We simultaneously add the boolean valued `List.lex` function,
parameterised by a `BEq` typeclass
and an arbitrary `lt` function. This will support the flexibility
previously provided for `List.lt`,
via a `==` function which is weaker than strict equality.
This PR introduces the basic theory of permutations of `Array`s and
proves `Array.swap_perm`.
The API falls well short of what is available for `List` at this point.
This PR upstreams the definition and basic lemmas about `List.finRange`
from Batteries.
Thanks for contributors to Batteries and Mathlib who've previously
worked on this material. Further PRs are welcome here. I'll be adding
more API later.
This PR changes the signature of `Array.set` to take a `Nat`, and a
tactic-provided bound, rather than a `Fin`.
Corresponding changes (but without the auto-param) for `Array.get` will
arrive shortly, after which I'll go more pervasively through the Array
API.
