diff --git a/gtsam_unstable/nonlinear/Expression-inl.h b/gtsam_unstable/nonlinear/Expression-inl.h
index f49b985ba..40fc54751 100644
--- a/gtsam_unstable/nonlinear/Expression-inl.h
+++ b/gtsam_unstable/nonlinear/Expression-inl.h
@@ -64,7 +64,8 @@ public:
   }
   /// Access via key
   VerticalBlockMatrix::Block operator()(Key key) {
-    FastVector<Key>::const_iterator it = std::find(keys_.begin(),keys_.end(),key);
+    FastVector<Key>::const_iterator it = std::find(keys_.begin(), keys_.end(),
+        key);
     DenseIndex block = it - keys_.begin();
     return Ab_(block);
   }
@@ -98,7 +99,7 @@ struct CallRecord {
 template<int ROWS, int COLS>
 void handleLeafCase(const Eigen::Matrix<double, ROWS, COLS>& dTdA,
     JacobianMap& jacobians, Key key) {
-  jacobians(key).block < ROWS, COLS > (0, 0) += dTdA; // block makes HUGE difference
+  jacobians(key).block<ROWS, COLS>(0, 0) += dTdA; // block makes HUGE difference
 }
 /// Handle Leaf Case for Dynamic Matrix type (slower)
 template<>
@@ -311,9 +312,9 @@ public:
 
 //-----------------------------------------------------------------------------
 /// Leaf Expression
-template<class T, class Chart=DefaultChart<T> >
+template<class T, class Chart = DefaultChart<T> >
 class LeafExpression: public ExpressionNode<T> {
-  typedef ChartValue<T,Chart> value_type; // perhaps this can be something else like a std::pair<T,Chart> ??
+  typedef ChartValue<T, Chart> value_type; // perhaps this can be something else like a std::pair<T,Chart> ??
 
   /// The key into values
   Key key_;
@@ -347,8 +348,8 @@ public:
   }
 
   /// Construct an execution trace for reverse AD
-  virtual const value_type& traceExecution(const Values& values, ExecutionTrace<value_type>& trace,
-      char* raw) const {
+  virtual const value_type& traceExecution(const Values& values,
+      ExecutionTrace<value_type>& trace, char* raw) const {
     trace.setLeaf(key_);
     return dynamic_cast<const value_type&>(values.at(key_));
   }
@@ -358,7 +359,7 @@ public:
 //-----------------------------------------------------------------------------
 /// Leaf Expression, if no chart is given, assume default chart and value_type is just the plain value
 template<typename T>
-class LeafExpression<T, DefaultChart<T> >: public ExpressionNode<T> {
+class LeafExpression<T, DefaultChart<T> > : public ExpressionNode<T> {
   typedef T value_type;
 
   /// The key into values
@@ -405,6 +406,7 @@ public:
 //   C++ Template Metaprogramming: Concepts, Tools, and Techniques from Boost
 //   and Beyond. Abrahams, David; Gurtovoy, Aleksey. Pearson Education.
 // to recursively generate a class, that will be the base for function nodes.
+//
 // The class generated, for three arguments A1, A2, and A3 will be
 //
 // struct Base1 : Argument<T,A1,1>, FunctionalBase<T> {
@@ -429,6 +431,30 @@ public:
 //
 // All this magic happens when  we generate the Base3 base class of FunctionalNode
 // by invoking boost::mpl::fold over the meta-function GenerateFunctionalNode
+//
+// Similarly, the inner Record struct will be
+//
+// struct Record1 : JacobianTrace<T,A1,1>, CallRecord<traits::dimension<T>::value> {
+//   ... storage related to A1 ...
+//   ... methods that work on A1 ...
+// };
+//
+// struct Record2 : JacobianTrace<T,A2,2>, Record1 {
+//   ... storage related to A2 ...
+//   ... methods that work on A2 and (recursively) on A1 ...
+// };
+//
+// struct Record3 : JacobianTrace<T,A3,3>, Record2 {
+//   ... storage related to A3 ...
+//   ... methods that work on A3 and (recursively) on A2 and A1 ...
+// };
+//
+// struct Record : Record3 {
+//   Provides convenience access to storage in hierarchy by using
+//   static_cast<JacobianTrace<T, A, N> &>(*this)
+// }
+//
+
 //-----------------------------------------------------------------------------
 
 /// meta-function to generate fixed-size JacobianTA type
@@ -457,6 +483,7 @@ struct FunctionalBase: ExpressionNode<T> {
 
   /// Construct an execution trace for reverse AD
   void trace(const Values& values, Record* record, char*& raw) const {
+    // base case: does not do anything
   }
 };
 
@@ -562,15 +589,23 @@ struct GenerateFunctionalNode: Argument<T, A, Base::N + 1>, Base {
 template<class T, class TYPES>
 struct FunctionalNode {
 
+  /// The following typedef generates the recursively defined Base class
   typedef typename boost::mpl::fold<TYPES, FunctionalBase<T>,
       GenerateFunctionalNode<T, MPL::_2, MPL::_1> >::type Base;
 
+  /**
+   *  The type generated by this meta-function derives from Base
+   *  and adds access functions as well as the crucial [trace] function
+   */
   struct type: public Base {
 
     // Argument types and derived, note these are base 0 !
+    // These are currently not used - useful for Phoenix in future
+#ifdef EXPRESSIONS_PHOENIX
     typedef TYPES Arguments;
     typedef typename boost::mpl::transform<TYPES, Jacobian<T, MPL::_1> >::type Jacobians;
     typedef typename boost::mpl::transform<TYPES, OptionalJacobian<T, MPL::_1> >::type Optionals;
+#endif
 
     /// Reset expression shared pointer
     template<class A, size_t N>
@@ -725,7 +760,8 @@ public:
 
   typedef boost::function<
       T(const A1&, const A2&, const A3&, typename OptionalJacobian<T, A1>::type,
-          typename OptionalJacobian<T, A2>::type, typename OptionalJacobian<T, A3>::type)> Function;
+          typename OptionalJacobian<T, A2>::type,
+          typename OptionalJacobian<T, A3>::type)> Function;
   typedef typename FunctionalNode<T, boost::mpl::vector<A1, A2, A3> >::type Base;
   typedef typename Base::Record Record;