diff --git a/gtsam/base/DSF.h b/gtsam/base/DSF.h
index 09b8fa332..af78db45c 100644
--- a/gtsam/base/DSF.h
+++ b/gtsam/base/DSF.h
@@ -50,6 +50,9 @@ namespace gtsam {
 		// constructor with a list of unconnected keys
 		DSF(const std::list<KEY>& keys) : Tree() { BOOST_FOREACH(const KEY& key, keys) *this = this->add(key, key); }
 
+		// constructor with a set of unconnected keys
+		DSF(const std::set<KEY>& keys) : Tree() { BOOST_FOREACH(const KEY& key, keys) *this = this->add(key, key); }
+
 		// create a new singleton, does nothing if already exists
 		Self makeSet(const KEY& key) const { if (mem(key)) return *this; else return this->add(key, key); }
 
diff --git a/gtsam/base/FastSet.h b/gtsam/base/FastSet.h
index 6007dae9b..391521ecc 100644
--- a/gtsam/base/FastSet.h
+++ b/gtsam/base/FastSet.h
@@ -18,7 +18,7 @@
 
 #pragma once
 
-#include <map>
+#include <set>
 #include <boost/pool/pool_alloc.hpp>
 
 namespace gtsam {
diff --git a/gtsam/base/blockMatrices.h b/gtsam/base/blockMatrices.h
index 5823b1365..445b88df2 100644
--- a/gtsam/base/blockMatrices.h
+++ b/gtsam/base/blockMatrices.h
@@ -93,11 +93,13 @@ public:
   typedef BlockColumn<const MATRIX> constColumn;
 
 protected:
-  FullMatrix& matrix_;
-  std::vector<size_t> variableColOffsets_;
-  size_t rowStart_;
-  size_t rowEnd_;
-  size_t blockStart_;
+  FullMatrix& matrix_; // the reference to the original matrix
+  std::vector<size_t> variableColOffsets_; // the starting columns of each block (0-based)
+
+  // for elimination, represent
+  size_t rowStart_; // 0 initially
+  size_t rowEnd_; // the number of row - 1, initially
+  size_t blockStart_; // 0 initially
 
 public:
   /** Construct from an empty matrix (asserts that the matrix is empty) */
diff --git a/gtsam/linear/GaussianFactor.h b/gtsam/linear/GaussianFactor.h
index fef2d4e94..4b370a606 100644
--- a/gtsam/linear/GaussianFactor.h
+++ b/gtsam/linear/GaussianFactor.h
@@ -75,8 +75,8 @@ public:
 
 	SharedDiagonal model_; // Gaussian noise model with diagonal covariance matrix
 	std::vector<size_t> firstNonzeroBlocks_;
-	AbMatrix matrix_;
-	BlockAb Ab_;
+	AbMatrix matrix_; // the full matrix correponding to the factor
+	BlockAb Ab_; // the block view of the full matrix
 
 public: