diff --git a/deferred_planarity_test/include/mps.h b/deferred_planarity_test/include/mps.h
index 4a99594..b86f430 100644
--- a/deferred_planarity_test/include/mps.h
+++ b/deferred_planarity_test/include/mps.h
@@ -33,6 +33,12 @@ enum node_type {
 	AE_VIRTUAL_ROOT = 3
 };
 
+enum mark_type {
+    UNMARKED = 0,
+    MARKED = 1,
+    RESERVED = 2,
+};
+
 class node
 {
 public:
@@ -116,7 +122,6 @@ public:
 
 	//MARK
 	void mark();
-	static void init_mark();
 	void un_mark();
 	bool is_marked();
 
@@ -146,8 +151,7 @@ private:
 	vector<node*> _essential_list;
 
 	//Mark
-	int _mark;
-	static int _ref_mark;
+	mark_type _mark;
 };
 
 class maximal_planar_subgraph_finder
diff --git a/deferred_planarity_test/makefile b/deferred_planarity_test/makefile
index 8a8fac8..d4b8ada 100644
--- a/deferred_planarity_test/makefile
+++ b/deferred_planarity_test/makefile
@@ -31,4 +31,4 @@ $(BIN_DIR) $(OBJ_DIR):
 
 .PHONY: clean
 clean:
-	rm -r $(BIN_DIR) $(OBJ_DIR)
+	rm -r $(OBJ_DIR)
diff --git a/deferred_planarity_test/src/main.cpp b/deferred_planarity_test/src/main.cpp
index acb33a7..d553325 100644
--- a/deferred_planarity_test/src/main.cpp
+++ b/deferred_planarity_test/src/main.cpp
@@ -13,7 +13,6 @@
 #include <vector>
  
 #include <ogdf/fileformats/GraphIO.h>
-#define START_TEMP 100
 
 using namespace std;
 
diff --git a/deferred_planarity_test/src/mps.cpp b/deferred_planarity_test/src/mps.cpp
index 0c07fbd..f93a52c 100644
--- a/deferred_planarity_test/src/mps.cpp
+++ b/deferred_planarity_test/src/mps.cpp
@@ -34,7 +34,13 @@ maximal_planar_subgraph_finder::return_post_order() {
 //Determine the post-order-list by a DFS-traversal.
 void
 maximal_planar_subgraph_finder::postOrderTraversal() {
-	node::init_mark();
+	// node::init_mark(); // set ref_mark 
+
+    // print out the ref_mark
+    // std::cout << "normal post order traversal" << std::endl;
+    // std::cout << "the ref mark is initialized to be:" << std::endl;
+    // _node_list[0]->print_ref_mark();
+
     // always start with node 0
 	int postOrderID = 0;
 	for (int i = 0; i < _node_list.size(); ++i) {
@@ -50,7 +56,7 @@ maximal_planar_subgraph_finder::postOrderTraversal() {
 // return is by reference via _post_order_list
 void 
 maximal_planar_subgraph_finder::guidedPostOrderTraversal(vector<int> post_order) {
-	node::init_mark();
+	// node::init_mark();
 
     vector<int> rev_post_order;
     for (int i = post_order.size() - 1; i >= 0; --i) {
@@ -86,7 +92,7 @@ maximal_planar_subgraph_finder::guidedPostOrderTraversal(vector<int> post_order)
 // return is by reference via _post_order_list
 void
 maximal_planar_subgraph_finder::mutatedPostOrderTraversal(vector<int> post_order, int mutate_point) {
-	node::init_mark();
+	// node::init_mark();
 
     vector<int> rev_post_order;
     for (int i = post_order.size() - 1; i >= 0; --i) {
diff --git a/deferred_planarity_test/src/node.cpp b/deferred_planarity_test/src/node.cpp
index 6ce6378..1e6c7d9 100644
--- a/deferred_planarity_test/src/node.cpp
+++ b/deferred_planarity_test/src/node.cpp
@@ -5,7 +5,7 @@
 #include "mps.h"
 
 // #define DEBUG
-#define DEBUG_MUTATION
+// #define DEBUG_MUTATION
 
 //-----------------------------------------------------------------------------------
 // CONSTRUCTOR
@@ -20,7 +20,7 @@ node::node(node_type t) {
 	_parent = 0;
 	_post_order_index = INT_MAX;
 	_node_id = INT_MAX;
-	_mark = 0;
+	_mark = UNMARKED;
 }
 
 //-----------------------------------------------------------------------------------
@@ -57,7 +57,7 @@ node* node::adj(int i) {return _adj_list[i];}
 void node::set_adj_list(vector<node*> vec) {_adj_list = vec;}
 
 void node::DFS_visit(vector<node*> &dfsList, int &index) {
-	mark();
+	mark(); // set _mark to _ref_mark
 	for (int i = 0; i < _adj_list.size(); ++i) {
 		if (!_adj_list[i]->is_marked()) {
 			_adj_list[i]->_parent = this;
@@ -358,12 +358,8 @@ void node::add_essential(node* u) {_essential_list.push_back(u);}
 //-----------------------------------------------------------------------------------
 // MARK
 //-----------------------------------------------------------------------------------
-void node::mark() {_mark = _ref_mark;}
+void node::mark() {_mark = MARKED;}
 
-void node::init_mark() {++_ref_mark;}
+void node::un_mark() {_mark = UNMARKED;}
 
-void node::un_mark() {_mark = 0;}
-
-bool node::is_marked() {return _mark == _ref_mark;}
-
-int node::_ref_mark = 1;
+bool node::is_marked() {return _mark == MARKED;}
\ No newline at end of file