This PR re-enables star-indexed lemmas as a fallback for `exact?` and
`apply?`.
Star-indexed lemmas (those with overly-general discrimination tree keys
like `[*]`)
were previously dropped entirely for performance reasons. This caused
useful lemmas
like `Empty.elim`, `And.left`, `not_not.mp`, `Sum.elim`, and
`Function.mtr` to be
unfindable by library search.
The implementation adds a two-pass search strategy:
1. First, search using concrete discrimination keys (the current
behavior)
2. If no results are found, fall back to trying star-indexed lemmas
The star-indexed lemmas are extracted during tree initialization and
cached in an
environment extension, avoiding repeated computation.
Users can disable the fallback with `-star`:
```lean
example {α : Sort u} (h : Empty) : α := by apply? -star -- error: no lemmas found
example {α : Sort u} (h : Empty) : α := by apply? -- finds Empty.elim
```
🤖 Prepared with Claude Code
---------
Co-authored-by: Claude <noreply@anthropic.com>
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