This PR ensures users can select the "minimal indexable subexpression"
condition in `grind` parameters. Example, they can now write `grind [!
-> thmName]`. `grind?` will include the `!` modifier whenever users had
used `@[grind!]`. This PR also fixes a missing case in the new pattern
inference procedure.
It also adjusts some `grind` annotations and tests in preparation for
setting the new pattern inference heuristic as the new default.
This PR moves `String.utf8EncodeChar` to the prelude to prepare for the
imminent redefinition of `String`.
The definition in the prelude uses modulo and division operations on
natural numbers. In `String.Extra`, a `csimp` lemma is provided, showing
that the new definition is equal to the previous one (which is now
called `utf8EncodeCharFast`) which uses bitwise operations on `UInt8`.
This PR eliminates uses of `intros x y z` (with arguments) and updates
the `intros` docstring to suggest that `intro x y z` should be used
instead. The `intros` tactic is historical, and can be traced all the
way back to Lean 2, when `intro` could only introduce a single
hypothesis. Since 2020, the `intro` tactic has superceded it. The
`intros` tactic (without arguments) is currently still useful.
This PR tries to improve the E-matching pattern inference for `grind`.
That said, we still need better tools for annotating and maintaining
`grind` annotations in libraries.
closes#9125
