void recordChange(Instruction instruction, TrackingDfaMemoryState previous) {
    Map<DfaVariableValue, Change> result = getChangeMap(previous);
    DfaValue value = isEmptyStack() ? getFactory().getUnknown() : peek();
    myHistory = MemoryStateChange.create(myHistory, instruction, result, value);
  }
void recordChange(Instruction instruction, TrackingDfaMemoryState previous)