diff --git a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillel.kt b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillel.kt
index faac46ad..c2ac3ecc 100644
--- a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillel.kt
+++ b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillel.kt
@@ -4,11 +4,13 @@ import ai.hypergraph.kaliningraph.types.*
 import kotlin.math.absoluteValue
 import kotlin.time.TimeSource
 
-infix fun FSA.intersectLevFSA(cfg: CFG) = cfg.intersectLevFSA(this)
+infix fun FSA.intersectLevFSA(cfg: CFG) = cfg.freeze().intersectLevFSAP(this)
 // http://www.cs.umd.edu/~gasarch/BLOGPAPERS/cfg.pdf#page=2
 // https://browse.arxiv.org/pdf/2209.06809.pdf#page=5
 
-infix fun CFG.intersectLevFSA(fsa: FSA): CFG {
+infix fun CFG.intersectLevFSA(fsa: FSA): CFG = freeze().intersectLevFSAP(fsa)
+
+private infix fun CFG.intersectLevFSAP(fsa: FSA): CFG {
   var clock = TimeSource.Monotonic.markNow()
   val initFinal =
     (fsa.init * fsa.final).map { (q, r) -> "START -> [$q,START,$r]" }
@@ -82,6 +84,7 @@ fun List<Σᐩ>.postProcess() =
     .also { println("∩-grammar has ${it.size} total productions") }
     .dropVestigialProductions().normalForm.noNonterminalStubs
     .also { println("∩-grammar has ${it.size} useful productions") }
+    .freeze()
     //    .also { println(it.pretty) }
     //    .also { println(it.size) }
 
@@ -110,7 +113,7 @@ fun CFG.dropVestigialProductions(
 //  val reachable = reachableSymbols()
   val rw = toMutableSet()
     .apply { removeAll { prod -> prod.RHS.any { criteria(it) && it !in nts } } }
-    .removeUselessSymbols()
+    .freeze().removeUselessSymbols()
 
   println("Removed ${size - rw.size} vestigial productions.")
 
diff --git a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Normalization.kt b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Normalization.kt
index 82548707..23247856 100644
--- a/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Normalization.kt
+++ b/src/commonMain/kotlin/ai/hypergraph/kaliningraph/parsing/Normalization.kt
@@ -212,7 +212,7 @@ fun CFG.genSym(from: Set<Σᐩ> = terminalUnitProductions.map { it.LHS }.toSet()
     val t = nextGenerating.first()
     nextGenerating.remove(t)
     allGenerating += t
-    nextGenerating += (bimap.TDEPS[t]?: emptyList())
+    nextGenerating += (bimap.TDEPS[t] ?: emptyList())
       .filter { it !in allGenerating && it !in nextGenerating }
   } while (nextGenerating.isNotEmpty())
 
diff --git a/src/commonTest/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillelTest.kt b/src/commonTest/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillelTest.kt
index daf3ffc3..d9c2b50a 100644
--- a/src/commonTest/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillelTest.kt
+++ b/src/commonTest/kotlin/ai/hypergraph/kaliningraph/parsing/BarHillelTest.kt
@@ -192,12 +192,14 @@ class BarHillelTest {
   @Test
   fun testPythonBarHillel() {
     val gram = Grammars.seq2parsePythonCFG.noEpsilonOrNonterminalStubs
-    val levBall = makeLevFSA("- NUMBER + NEWLINE", 2, gram.terminals)
+    val toRepair = "NAME = ( NAME .".tokenizeByWhitespace()
+    val levBall = makeLevFSA(toRepair, 3, gram.terminals)
     val intGram = gram.intersectLevFSA(levBall)
-      .also { println("LEV ∩ CFG grammar:\n${it.pretty}") }
+//      .also { println("LEV ∩ CFG grammar:\n${it.pretty}") }
     val clock = TimeSource.Monotonic.markNow()
 
-    val lbhSet = intGram.enumSeq(List(6) { "_" }.joinToString(" "))
+    val template = List(toRepair.size + 2) { "_" }.joinToString(" ")
+    val lbhSet = intGram.enumSeq(template)
       .onEach {
         println(it)
         assertTrue(it in gram.language)