# Slime Reverse Search Experiment

This folder is for experiments that search "backwards" from a desired slime
chunk pattern instead of scanning every `(seed, x, z)` tuple directly.

## SMT Bit-Vector Prototype

`slime_reverse_smt.py` emits an SMT-LIB query with these variables:

- `seed48`: the low 48 bits of the world seed
- `chunkX`, `chunkZ`: the top-left chunk coordinate, unless fixed with `--x/--z`

It uses the approximate predicate:

```text
((LCG48(seed48 + coordTerm(x, z)) >> 17) % 10) == 0
```

That removes Java `nextInt(10)`'s extremely rare rejection-loop branch.  Models
from this query are candidates and should be verified with the exact predicate.

Examples:

```bash
# Generate a 4x4 query with variable coordinates in [-64, 64].
python3 exp/slime_reverse_smt.py -n 4 -r 64 -o /tmp/slime4.smt2
z3 /tmp/slime4.smt2

# Fix the top-left coordinate and solve only for seed48.
python3 exp/slime_reverse_smt.py -n 4 --x 0 --z 0 --run --verify

# Start with a cheaper partial query before asking for all cells.
python3 exp/slime_reverse_smt.py -n 5 -r 128 --cells border --run --verify
python3 exp/slime_reverse_smt.py -n 5 -r 128 --cells corners --run
```

Notes:

- Variable `chunkX/chunkZ` introduce bit-vector multiplication, so large-radius
  full 5x5 queries may be very hard for a solver.
- Fixed-coordinate queries are much cleaner and are useful for testing whether a
  solver can handle many seed constraints.
- Exact verification is included because the SMT predicate intentionally ignores
  Java's rejection retry.