diff --git a/src/GC/Makefile b/src/GC/Makefile
index b99d2a4..00389c3 100644
--- a/src/GC/Makefile
+++ b/src/GC/Makefile
@@ -36,8 +36,7 @@ linker_vg:
 	valgrind $(VGFLAGS) tests/linker.out
 
 extern_lib:
-	rm -f lib/heap.o
-	rm -f lib/libheap.so
+	rm -f lib/heap.o lib/libheap.so tests/extern_lib.out
 	$(CC) $(STDFLAGS) -c -fPIC -o lib/heap.o lib/heap.cpp
 	$(CC) $(STDFLAGS) -shared -o lib/libheap.so lib/heap.o
 	$(CC) $(LIB_INCL) $(LIB_SO) -v -Wall -o tests/extern_lib.out tests/extern_lib.cpp
\ No newline at end of file
diff --git a/src/GC/lib/heap.cpp b/src/GC/lib/heap.cpp
index a222833..d13cec6 100644
--- a/src/GC/lib/heap.cpp
+++ b/src/GC/lib/heap.cpp
@@ -20,6 +20,7 @@ namespace GC {
   */
   void Heap::check_init() {
     auto heap = Heap::the();
+    cout << "Heap addr:\t" << heap << endl;
     cout << "GC m_stack_end:\t" << heap->m_stack_end << endl;
     auto stack_start = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
     cout << "GC stack_start:\t" << stack_start << endl;
@@ -172,10 +173,11 @@ namespace GC {
     if (heap->m_stack_end != nullptr)
       stack_end = heap->m_stack_end;
     else
-      stack_end = (uintptr_t *) stack_start - 40; // dummy value
+      stack_end = (uintptr_t *) stack_start - 80; // dummy value
 
+    cout << "Stack end in collect: " << stack_end << endl;
     auto work_list = heap->m_allocated_chunks;
-    // print_worklist(work_list);
+    //print_worklist(work_list);
 
     if (flags & MARK) {
       mark(stack_start, stack_end, work_list);
@@ -210,20 +212,58 @@ namespace GC {
   void Heap::mark(uintptr_t *start, const uintptr_t *end, vector<Chunk*> worklist) {
     for (; start > end; start--) { // to find adresses thats in the worklist
       if (*start % 8 == 0) { // all pointers must be aligned as double words
-        for (size_t i = 0; i < worklist.size(); i++) { // fix this
-          auto chunk = worklist.at(i);
+        for (auto it = worklist.begin(); it != worklist.end();) {
+        //for (size_t i = 0; i < worklist.size(); i++) { // fix this
+          //auto chunk = worklist.at(i);
+          auto chunk = *it;
           uintptr_t c_start = reinterpret_cast<uintptr_t>(chunk->start);
           uintptr_t c_end = reinterpret_cast<uintptr_t>(chunk->start + chunk->size);
           if (c_start <= *start && *start < c_end) {
             uintptr_t c_start = reinterpret_cast<uintptr_t>(chunk->start);
             if (!chunk->marked) {
               chunk->marked = true;
-              worklist.erase(worklist.begin() + i);
-              auto new_stack_start = reinterpret_cast<uintptr_t *>(start);
-              mark(new_stack_start, end, worklist); //
-              return;
+              //worklist.erase(worklist.begin() + i);
+              it = worklist.erase(it);
+              //auto new_stack_start = reinterpret_cast<uintptr_t *>(start);
+              //mark(new_stack_start, end, worklist); //
+              //return;
+            }
+            else {
+              ++it;
             }
           }
+          else {
+            ++it;
+          }
+        }
+      }
+    }
+  }
+
+  // Mark child references from the root references
+  void mark_test(vector<Chunk *> worklist) {
+    while (worklist.size() > 0) {
+      Chunk *ref = worklist.back();
+      worklist.pop_back();
+      Chunk *child = (Chunk*) ref; // this is probably not correct
+      if (child != nullptr && !child->marked) {
+        child->marked = true;
+        worklist.push_back(child);
+        mark_test(worklist);
+      }
+    }
+  }
+
+  // Mark the root references and look for child references to them
+  void mark_from_roots(uintptr_t *start, const uintptr_t *end) {
+    vector<Chunk *> worklist;
+    for (;start > end; start --) {
+      if (*start % 8 == 0) { // all pointers must be aligned as double words
+        Chunk *ref = (Chunk*) *start;
+        if (ref != nullptr && !ref->marked) {
+          ref->marked = true;
+          worklist.push_back(ref);
+          //mark_test(worklist)
         }
       }
     }
diff --git a/src/GC/lib/heap.o b/src/GC/lib/heap.o
index 2f2a154..0e5421d 100644
Binary files a/src/GC/lib/heap.o and b/src/GC/lib/heap.o differ
diff --git a/src/GC/lib/libheap.so b/src/GC/lib/libheap.so
index 83a12f5..4e7c0eb 100755
Binary files a/src/GC/lib/libheap.so and b/src/GC/lib/libheap.so differ
diff --git a/src/GC/tests/extern_lib.cpp b/src/GC/tests/extern_lib.cpp
index 5f3e0c7..2d47576 100644
--- a/src/GC/tests/extern_lib.cpp
+++ b/src/GC/tests/extern_lib.cpp
@@ -3,11 +3,9 @@
 
 #include "heap.hpp"
 
-// using namespace std;
-
-// GC::Heap *singleton_test();
-// void init_gc(GC::Heap *heap);
-// void frame_test(GC::Heap *heap);
+GC::Heap *singleton_test();
+void init_gc(GC::Heap *heap);
+void frame_test(GC::Heap *heap);
 
 GC::Heap *singleton_test() {
     std::cout << "TESTING SINGLETON INSTANCES" << std::endl;
@@ -38,11 +36,13 @@ void frame_test(GC::Heap *heap) {
     std::cout << "Previous stack frame:\t" << prev_frame << std::endl;
 
     heap->check_init();
+    // auto alloced = heap->alloc(sizeof(unsigned long));
     
     std::cout << "===========================" << std::endl;
 }
 
 int main() {
+    std::cout << "in main" << std::endl;
     auto heap = singleton_test();
 
     init_gc(heap);
diff --git a/src/GC/tests/h_test.cpp b/src/GC/tests/h_test.cpp
index 774f091..65f51d6 100644
--- a/src/GC/tests/h_test.cpp
+++ b/src/GC/tests/h_test.cpp
@@ -2,21 +2,34 @@
 
 GC::Heap *gc = GC::Heap::the();
 
+/* void assign(int *dst) {
+    int *local = static_cast<int *>(gc->alloc(sizeof(int)));
+    *local = 10;
+    dst = reinterpret_cast<int **>(dst);
+    *dst = local;
+} */
+
 void init() {
 
     auto stack_start = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
-    auto stack_end = stack_start - 40;
+    //auto stack_end = stack_start - 40;
     std::cout << "Stack start from init:\t" << stack_start << std::endl;
-    std::cout << "Imaginary stack end:\t" << stack_end << std::endl;
+    //std::cout << "Imaginary stack end:\t" << stack_end << std::endl;
     int *arr = static_cast<int *>(gc->alloc(sizeof(int) * 100));
-    std::cout << "Arr_ptr" << std::hex << arr << "\n\n\n" << std::endl;
+    //std::cout << "Arr_ptr" << std::hex << arr << "\n\n\n" << std::endl;
     for (int i = 0; i < (sizeof(int) * 100); i++) {
         arr[i] = i;
     }
-    std::cout << "First stack pointer:\t" << &arr << std::endl;
+    for (int i = 0; i < (sizeof(int) * 20); i++) {
+        gc->alloc(sizeof(int));
+    }
+    std::cout << "Pointer for arr:\t" << &arr << std::endl;
     long a = 20;
     long *l = static_cast<long *>(gc->alloc(sizeof(long)));
-    l = &a;
+    std::cout << "Pointer for l:\t\t" << &l << std::endl;
+    int *i = static_cast<int *>(gc->alloc(sizeof(int)));
+    std::cout << "Pointer for i:\t\t" << &i << std::endl;
+    //l = &a;
     //*l = 20;
 }
 
@@ -24,7 +37,7 @@ int main() {
     auto stack_start = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
     std::cout << "Stack start from main:\t" << stack_start << std::endl;
     init();
-    gc->collect(MARK | SWEEP | FREE);
+    gc->collect(MARK | SWEEP); // some bug in free (vector out of range)
     gc->print_contents();
     //delete gc;
     return 0;