Extends evals/deductive_logic/grounding.py from unary predicates / single-var rules to
binary relations + multi-variable universal rules, still by FINITE PROPOSITIONAL
grounding into the regime the ROBDD engine + the independent truth-table oracle both
decide. wrong==0 stays structural. This is the real capability step a RuleTaker/
ProofWriter-style mirror needs (the unary fragment alone is trivial).
- atom_n lowers pred(a,b) -> pred__a__b; arity-1 is byte-identical to the old atom, so
the live unary panel lowers unchanged (proven by an exact-string back-compat test).
- multi-variable universal rules ground over n^k assignments — transitivity now decides.
- range-restriction: a rule with a head variable unbound in the body refuses (unsafe_rule)
— it grounds soundly but is outside the clean regime real benchmarks use.
- typed refusals: arity>=3/functions, explicit quantifiers, variable-free rules, bounds.
Honest ceilings (documented in docs/analysis/relational-grounding-extension-2026-06-04.md):
- THE binding constraint is the GOLD, not the grammar: the truth-table oracle is
O(2^atoms), so grounding refuses above MAX_GROUND_ATOMS=20 => binary problems cap at
~4 entities/predicate. A real lift needs a 2nd genuinely-independent sub-enumeration
oracle (not built).
- OPEN-WORLD only: RuleTaker/ProofWriter's main splits are closed-world + NAF; a future
adapter MUST refuse CWA/NAF (mapping CWA "False"->"refuted" is a wrong=0 breach).
- arity <= 2, function-free.
Validated: held-out differential fuzz (400 random binary problems, oracle-golded) = 0
engine/oracle mismatches; unary back-compat byte-identical; INV-25b reproducibility green;
deductive lane wrong=0 16/16; smoke 87.
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