diff --git a/data_structures/skiplist/skiplist.hpp b/data_structures/skiplist/skiplist.hpp
index 770d0602e..2446ab00f 100644
--- a/data_structures/skiplist/skiplist.hpp
+++ b/data_structures/skiplist/skiplist.hpp
@@ -110,7 +110,8 @@ public:
      */
     struct Flags
     {
-        enum node_flags : uint8_t {
+        enum node_flags : uint8_t
+        {
             MARKED       = 0x01,
             FULLY_LINKED = 0x10,
         };
@@ -274,9 +275,12 @@ public:
     class ConstIterator : public IteratorBase<ConstIterator>
     {
         friend class SkipList;
-        using IteratorBase<ConstIterator>::IteratorBase;
+        ConstIterator(Node* node) : IteratorBase<ConstIterator>(node) {}
 
     public:
+        ConstIterator() = default;
+        ConstIterator(const ConstIterator&) = default;
+
         const value_type& operator*()
         {
             return IteratorBase<ConstIterator>::operator*();
@@ -296,7 +300,11 @@ public:
     class Iterator : public IteratorBase<Iterator>
     {
         friend class SkipList;
-        using IteratorBase<Iterator>::IteratorBase;
+        Iterator(Node* node) : IteratorBase<Iterator>(node) {}
+
+    public:
+        Iterator() = default;
+        Iterator(const Iterator&) = default;
     };
 
     SkipList() : header(Node::create(K(), std::move(T()), H)) {}
@@ -307,74 +315,91 @@ public:
     {
         friend class SkipList;
 
-        Accessor(SkipList& skiplist) : skiplist(skiplist) {}
+        Accessor(SkipList* skiplist) : skiplist(skiplist)
+        {
+            assert(skiplist != nullptr);
+            // addref
+        }
+
     public:
         Accessor(const Accessor&) = delete;
-        Accessor(Accessor&&) = default;
+
+        Accessor(Accessor&& other) : skiplist(other.skiplist)
+        {
+            other.skiplist = nullptr;
+        }
+
+        ~Accessor()
+        {
+            if(skiplist == nullptr)
+                return;
+
+            // releaseref
+        }
 
         Iterator begin()
         {
-            return skiplist.begin();
+            return skiplist->begin();
         }
 
         ConstIterator begin() const
         {
-            return skiplist.cbegin();
+            return skiplist->cbegin();
         }
 
         ConstIterator cbegin() const
         {
-            return skiplist.cbegin();
+            return skiplist->cbegin();
         }
 
         Iterator end()
         {
-            return skiplist.end();
+            return skiplist->end();
         }
 
         ConstIterator end() const
         {
-            return skiplist.cend();
+            return skiplist->cend();
         }
 
         ConstIterator cend() const
         {
-            return skiplist.cend();
+            return skiplist->cend();
         }
 
         std::pair<Iterator, bool> insert_unique(const K& key, const T& item)
         {
-            return skiplist.insert({key, item}, preds, succs);
+            return skiplist->insert({key, item}, preds, succs);
         }
 
         std::pair<Iterator, bool> insert_unique(const K& key, T&& item)
         {
-            return skiplist.insert({key, std::forward<T>(item)}, preds, succs);
+            return skiplist->insert({key, std::forward<T>(item)}, preds, succs);
         }
 
         ConstIterator find(const K& key) const
         {
-            return skiplist.find(key);
+            return static_cast<const SkipList&>(*skiplist).find(key);
         }
 
         Iterator find(const K& key)
         {
-            return skiplist.find(key);
+            return skiplist->find(key);
         }
 
         bool remove(const K& key)
         {
-            return skiplist.remove(key, preds, succs);
+            return skiplist->remove(key, preds, succs);
         }
 
     private:
-        SkipList& skiplist;
+        SkipList* skiplist;
         Node* preds[H], *succs[H];
     };
 
     Accessor access()
     {
-        return Accessor(*this);
+        return Accessor(this);
     }
 
 private:
@@ -427,7 +452,7 @@ private:
 
     ConstIterator find(const K& key) const
     {
-        return find_node<ConstIterator>(key);
+        return const_cast<SkipList*>(this)->find_node<ConstIterator>(key);
     }
 
     Iterator find(const K& key)
diff --git a/data_structures/skiplist/skiplistset.hpp b/data_structures/skiplist/skiplistset.hpp
new file mode 100644
index 000000000..abf3f298d
--- /dev/null
+++ b/data_structures/skiplist/skiplistset.hpp
@@ -0,0 +1,229 @@
+#pragma once
+
+#include <cassert>
+
+#include "skiplist.hpp"
+#include "utils/total_ordering.hpp"
+
+template <class T, size_t H=32, class lock_t=SpinLock>
+class SkipListSet
+{
+    class Key : public TotalOrdering<Key>
+    {
+    public:
+        Key() = default;
+        Key(const T* item) : item(item) {}
+        Key(const T& item) : item(&item) {}
+
+        friend constexpr bool operator<(const Key& lhs, const Key& rhs)
+        {
+            assert(!lhs.empty());
+            assert(!rhs.empty());
+
+            return *lhs.item < *rhs.item;
+        }
+
+        friend constexpr bool operator==(const Key& lhs, const Key& rhs)
+        {
+            assert(!lhs.empty());
+            assert(!rhs.empty());
+
+            return *lhs.item == *rhs.item;
+        }
+
+        bool empty() const
+        {
+            return item == nullptr;
+        }
+
+        operator const T&() const
+        {
+            assert(item != nullptr);
+            return *item;
+        }
+
+    private:
+        const T* item {nullptr};
+    };
+
+    using skiplist_t = SkipList<Key, T, H, lock_t>;
+    using iter_t = typename skiplist_t::Iterator;
+    using const_iter_t = typename skiplist_t::ConstIterator;
+
+public:
+    template <class Derived, class It>
+    class IteratorBase : public Crtp<Derived>
+    {
+    protected:
+        IteratorBase(const It& it) : it(it) {}
+        IteratorBase(It&& it) : it(std::move(it)) {}
+
+        It it;
+    public:
+        IteratorBase() = default;
+        IteratorBase(const IteratorBase&) = default;
+
+        auto& operator*()
+        {
+            return it->second;
+        }
+
+        auto* operator->()
+        {
+            return &it->second;
+        }
+
+        operator T&()
+        {
+            return it->second;
+        }
+
+        Derived& operator++()
+        {
+            it++;
+            return this->derived();
+        }
+
+        Derived& operator++(int)
+        {
+            return operator++();
+        }
+
+        friend bool operator==(const Derived& a, const Derived& b)
+        {
+            return a.it == b.it;
+        }
+
+        friend bool operator!=(const Derived& a, const Derived& b)
+        {
+            return !(a == b);
+        }
+    };
+
+    class ConstIterator : public IteratorBase<ConstIterator, const_iter_t>
+    {
+        friend class SkipListSet;
+
+        using Base = IteratorBase<ConstIterator, const_iter_t>;
+
+        ConstIterator(const const_iter_t& it) : Base(it) {}
+        ConstIterator(const_iter_t&& it) : Base(std::move(it)) {}
+
+    public:
+        ConstIterator() = default;
+        ConstIterator(const ConstIterator&) = default;
+
+        const T& operator*()
+        {
+            return Base::operator*();
+        }
+
+        const T* operator->()
+        {
+            return Base::operator->();
+        }
+
+        operator const T&()
+        {
+            return Base::operator T&();
+        }
+    };
+
+    class Iterator : public IteratorBase<Iterator, iter_t>
+    {
+        friend class SkipListSet;
+
+        using Base = IteratorBase<Iterator, iter_t>;
+
+        Iterator(const iter_t& it) : Base(it) {}
+        Iterator(iter_t&& it) : Base(std::move(it)) {}
+
+    public:
+        Iterator() = default;
+        Iterator(const Iterator&) = default;
+
+    };
+
+    SkipListSet() = default;
+
+    friend class Accessor;
+
+    class Accessor
+    {
+        friend class SkipListSet;
+
+        using accessor_t = typename skiplist_t::Accessor;
+        Accessor(accessor_t&& accessor) : accessor(std::move(accessor)) {}
+
+    public:
+        Accessor(const Accessor&) = delete;
+        Accessor(Accessor&&) = default;
+
+        Iterator begin()
+        {
+            return Iterator(accessor.begin());
+        }
+
+        ConstIterator begin() const
+        {
+            return ConstIterator(accessor.cbegin());
+        }
+
+        ConstIterator cbegin() const
+        {
+            return ConstIterator(accessor.cbegin());
+        }
+
+        Iterator end()
+        {
+            return Iterator(accessor.end());
+        }
+
+        ConstIterator end() const
+        {
+            return ConstIterator(accessor.cend());
+        }
+
+        ConstIterator cend() const
+        {
+            return ConstIterator(accessor.cend());
+        }
+
+        std::pair<Iterator, bool> insert(const T& item)
+        {
+            auto r = accessor.insert_unique(Key(item), item);
+            return { Iterator(r.first), r.second };
+        }
+
+        ConstIterator find(const T& item) const
+        {
+            return ConstIterator(accessor.find(Key(item)));
+        }
+
+        Iterator find(const T& item)
+        {
+            return Iterator(accessor.find(Key(item)));
+        }
+
+        bool contains(const T& item) const
+        {
+            return accessor.find(Key(item)) != accessor.end();
+        }
+
+        bool remove(const T& item)
+        {
+            return accessor.remove(Key(item));
+        }
+
+    private:
+        accessor_t accessor;
+    };
+
+    Accessor access()
+    {
+        return Accessor(std::move(data.access()));
+    }
+
+private:
+    SkipList<Key, T> data;
+};
diff --git a/examples/skiplistset.cpp b/examples/skiplistset.cpp
new file mode 100644
index 000000000..f85d17045
--- /dev/null
+++ b/examples/skiplistset.cpp
@@ -0,0 +1,54 @@
+#include <iostream>
+
+#include "data_structures/skiplist/skiplistset.hpp"
+
+using std::cout;
+using std::endl;
+
+void print_skiplist(const SkipListSet<int>::Accessor& skiplist)
+{
+    cout << "---- skiplist set now has: ";
+
+    for(auto& item : skiplist)
+        cout << item << ", ";
+
+    cout << "----" << endl;
+}
+
+int main(void)
+{
+    SkipListSet<int> set;
+    auto accessor = set.access();
+
+    cout << std::boolalpha;
+
+    cout << "added non-existing 1? (true) "
+         << accessor.insert(1).second << endl;
+
+    cout << "added already existing 1? (false) "
+         << accessor.insert(1).second << endl;
+
+    accessor.insert(2);
+    print_skiplist(accessor);
+
+    cout << "item 3 doesn't exist? (true) "
+         << (accessor.find(3) == accessor.end()) << endl;
+
+    cout << "item 3 exists? (false) "
+         << accessor.contains(3) << endl;
+
+    cout << "item 2 exists? (true) "
+         << (accessor.find(2) != accessor.end()) << endl;
+
+    cout << "at item 2 is? 2 " << *accessor.find(2) << endl;
+
+    cout << "removed existing 1? (true) " << accessor.remove(1) << endl;
+    cout << "removed non-existing 3? (false) " << accessor.remove(3) << endl;
+
+    accessor.insert(1);
+    accessor.insert(4);
+
+    print_skiplist(accessor);
+
+    return 0;
+}
diff --git a/storage/model/properties/property.hpp b/storage/model/properties/property.hpp
index 72a8bb599..b0a6ce105 100644
--- a/storage/model/properties/property.hpp
+++ b/storage/model/properties/property.hpp
@@ -11,8 +11,6 @@ struct Property
 
     enum class Flags : unsigned
     {
-        Null     = 0x1,
-
         Bool     = 0x2,
         True     = 0x4 | Bool,
         False    = 0x8 | Bool,
@@ -58,18 +56,6 @@ struct Property
     Flags flags;
 };
 
-struct Null : public Property
-{
-    static constexpr Flags type = Flags::Null;
-
-    Null() : Property(Flags::Null) {}
-
-    bool is_null()
-    {
-        return true;
-    }
-};
-
 struct Bool : public Property
 {
     static constexpr Flags type = Flags::Bool;
@@ -89,7 +75,7 @@ struct String : public Property
 {
     static constexpr Flags type = Flags::String;
 
-    String(const std::string& value) 
+    String(const std::string& value)
         : Property(Flags::String), value(value) {}
 
     String(std::string&& value)
@@ -102,7 +88,7 @@ struct Int32 : public Property
 {
     static constexpr Flags type = Flags::Int32;
 
-    Int32(int32_t value) 
+    Int32(int32_t value)
         : Property(Flags::Int32), value(value) {}
 
     int32_t value;
@@ -112,7 +98,7 @@ struct Int64 : public Property
 {
     static constexpr Flags type = Flags::Int64;
 
-    Int64(int64_t value) 
+    Int64(int64_t value)
         : Property(Flags::Int64), value(value) {}
 
     int64_t value;
@@ -122,7 +108,7 @@ struct Float : public Property
 {
     static constexpr Flags type = Flags::Float;
 
-    Float(float value) 
+    Float(float value)
         : Property(Flags::Float), value(value) {}
 
     float value;
@@ -132,7 +118,7 @@ struct Double : public Property
 {
     static constexpr Flags type = Flags::Double;
 
-    Double(double value) 
+    Double(double value)
         : Property(Flags::Double), value(value) {}
 
     double value;
@@ -143,7 +129,6 @@ void Property::accept(Handler& h)
 {
     switch(flags)
     {
-        case Flags::Null:   return h.handle(static_cast<Null&>(*this));
         case Flags::True:   return h.handle(static_cast<Bool&>(*this));
         case Flags::False:  return h.handle(static_cast<Bool&>(*this));
         case Flags::String: return h.handle(static_cast<String&>(*this));
diff --git a/utils/terminate_handler.hpp b/utils/terminate_handler.hpp
index b022cf5a2..294d31151 100644
--- a/utils/terminate_handler.hpp
+++ b/utils/terminate_handler.hpp
@@ -1,32 +1,48 @@
 #pragma once
 
+#include "utils/auto_scope.hpp"
+
 #include <iostream>
 #include <execinfo.h>
 
 // TODO: log to local file or remote database
-void stacktrace() noexcept
+void stacktrace(std::ostream& stream) noexcept
 {
-    void *array[50];
-    int size = backtrace(array, 50);    
-    std::cout << __FUNCTION__ << " backtrace returned " << size << " frames\n\n";
-    char **messages = backtrace_symbols(array, size);
-    for (int i = 0; i < size && messages != NULL; ++i) {
-        std::cout << "[bt]: (" << i << ") " << messages[i] << std::endl;
-    }
-    std::cout << std::endl;
-    free(messages);
+    void* array[50];
+    int size = backtrace(array, 50);
+
+    stream << __FUNCTION__ << " backtrace returned "
+           << size << " frames." << std::endl;
+
+    char** messages = backtrace_symbols(array, size);
+    Auto(free(messages));
+
+    for (int i = 0; i < size && messages != NULL; ++i)
+        stream << "[bt]: (" << i << ") " << messages[i] << std::endl;
+
+    stream << std::endl;
 }
 
 // TODO: log to local file or remote database
-void terminate_handler() noexcept
+void terminate_handler(std::ostream& stream) noexcept
 {
-    if (auto exc = std::current_exception()) { 
-        try {
+    if(auto exc = std::current_exception())
+    {
+        try
+        {
             std::rethrow_exception(exc);
-        } catch (std::exception &ex) {
-            std::cout << ex.what() << std::endl << std::endl;
-            stacktrace();
+        }
+        catch(std::exception& ex)
+        {
+            stream << ex.what() << std::endl << std::endl;
+            stacktrace(stream);
         }
     }
-    std::_Exit(EXIT_FAILURE);
+
+    std::abort();
+}
+
+void terminate_handler() noexcept
+{
+    terminate_handler(std::cout);
 }
diff --git a/utils/total_ordering.hpp b/utils/total_ordering.hpp
index 09651cf23..97f8871e3 100644
--- a/utils/total_ordering.hpp
+++ b/utils/total_ordering.hpp
@@ -3,22 +3,22 @@
 template <class Derived>
 struct TotalOrdering
 {
-    friend bool operator!=(const Derived& a, const Derived& b)
+    friend constexpr bool operator!=(const Derived& a, const Derived& b)
     {
         return !(a == b);
     }
 
-    friend bool operator<=(const Derived& a, const Derived& b)
+    friend constexpr bool operator<=(const Derived& a, const Derived& b)
     {
         return a < b || a == b;
     }
 
-    friend bool operator>(const Derived& a, const Derived& b)
+    friend constexpr bool operator>(const Derived& a, const Derived& b)
     {
         return !(a <= b);
     }
 
-    friend bool operator>=(const Derived& a, const Derived& b)
+    friend constexpr bool operator>=(const Derived& a, const Derived& b)
     {
         return !(a < b);
     }
diff --git a/utils/utils.hpp b/utils/utils.hpp
deleted file mode 100644
index b59f1d3b0..000000000
--- a/utils/utils.hpp
+++ /dev/null
@@ -1,4 +0,0 @@
-#pragma once
-
-#include "string/all.hpp"
-#include "sync/all.hpp"