This PR adds `solve_by_elim` as a fallback in the `try?` tactic's simple
tactics. When `rfl` and `assumption` both fail but `solve_by_elim`
succeeds (e.g., for goals requiring hypothesis chaining or
backtracking), `try?` will now suggest `solve_by_elim`.
The structure is `first | (attempt_all | rfl | assumption) |
solve_by_elim`, so `solve_by_elim` only runs when the faster tactics
fail.
This is a prerequisite for removing the "first pass" `solve_by_elim`
from `apply?`. Currently `apply?` calls `solve_by_elim` twice: once
before library search, and once after each lemma application. The first
pass can be removed once `try?` includes `solve_by_elim`.
🤖 Prepared with Claude Code
---------
Co-authored-by: Claude <noreply@anthropic.com>
This PR enables parallelism in `try?`. Currently, we replace the
`attempt_all` stages (there are two, one for builtin tactics including
`grind` and `simp_all`, and a second one for all user extensions) with
parallel versions. We do not (yet?) change the behaviour of `first`
based stages.
