diff --git a/src/main/scala/org/geneontology/rules/engine/ReteNodes.scala b/src/main/scala/org/geneontology/rules/engine/ReteNodes.scala
index 86dcc22..5e242f0 100644
--- a/src/main/scala/org/geneontology/rules/engine/ReteNodes.scala
+++ b/src/main/scala/org/geneontology/rules/engine/ReteNodes.scala
@@ -220,7 +220,6 @@ final class ProductionNode(rule: Rule, parent: BetaNode, engine: RuleEngine) ext
     for {
       pattern <- rule.head
     } {
-      //FIXME get rid of casting
       val newTriple = Triple(
         produceNode(pattern.s, token).asInstanceOf[Resource],
         produceNode(pattern.p, token).asInstanceOf[URI],
@@ -233,7 +232,7 @@ final class ProductionNode(rule: Rule, parent: BetaNode, engine: RuleEngine) ext
   private def produceNode(node: Node, token: Token): ConcreteNode = node match {
     case c: ConcreteNode => c
     case v: Variable     => token.bindings(v)
-    //case AnyNode => error
+    case AnyNode         => throw new RuntimeException("Invalid rule head containing AnyNode")
   }
 
   def addChild(node: BetaNode): Unit = ()
diff --git a/src/main/scala/org/geneontology/rules/engine/WorkingMemory.scala b/src/main/scala/org/geneontology/rules/engine/WorkingMemory.scala
index 8ce0495..3794cc1 100644
--- a/src/main/scala/org/geneontology/rules/engine/WorkingMemory.scala
+++ b/src/main/scala/org/geneontology/rules/engine/WorkingMemory.scala
@@ -4,7 +4,7 @@ import scala.collection.immutable.Queue
 import scala.collection.mutable
 import scala.collection.mutable.AnyRefMap
 
-final class WorkingMemory(var asserted: Set[Triple]) {
+final class WorkingMemory(val asserted: Set[Triple]) {
 
   var agenda: Queue[Triple] = Queue.empty
   val facts: mutable.Set[Triple] = mutable.Set.empty ++ asserted
@@ -60,7 +60,6 @@ final class BetaMemory(val spec: JoinNodeSpec, initialLinkedChildren: List[BetaN
   var tokens: List[Token] = Nil
   var checkRightLink: Boolean = true
   var checkLeftLink: Boolean = false
-  //val tokenIndex: mutable.Map[(Variable, ConcreteNode), mutable.Set[Token]] = AnyRefMap.empty
   val tokenIndex: mutable.Map[Variable, mutable.Map[ConcreteNode, List[Token]]] = AnyRefMap.empty
   var linkedChildren: List[BetaNode] = initialLinkedChildren