okay, bar-hillel works (just need to prune dangling NTs)

src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Normalization.kt

@@ -12,6 +12,18 @@ import ai.hypergraph.kaliningraph.types.*
 
 val rewriteHistory = LRUCache<CFG, List<CFG>>()
 
+// Recursively rmoves all productions containing a dangling nonterminal, i.e.,
+// a nonterminal from a synthetic CFG that does not produce any terminals.
+fun CFG.removeDanglingNonterminals(
+  matches: (Σᐩ) -> Boolean = { it.first() == '[' && it.last() == ']' && it.count { it == ',' } == 2 }
+): CFG {
+  val rw =
+    filter { it.RHS.all { !matches(it) || it in nonterminals } }
+    .toSet()
+
+  return if (rw.size == size) this else rw.removeDanglingNonterminals(matches)
+}
+
 /**
  * n.b. Normalization may destroy organic nonterminals!
  * In order to preserve every organic nonterminal, you
@@ -32,6 +44,7 @@ fun CFG.normalize(): CFG =
       // Must remember to run the unit test if order changes in the future
       // ./gradlew jvmTest --tests "ai.hypergraph.kaliningraph.sat.SATValiantTest.testTLArithmetic"
       .generateNonterminalStubs()
+      .removeDanglingNonterminals()
       .also { cnf -> rewriteHistory.put(cnf.freeze(), rewrites) }
   }