diff --git a/src/htmlparser/ElementNode.lua b/src/htmlparser/ElementNode.lua
index d249abb..5235a4c 100644
--- a/src/htmlparser/ElementNode.lua
+++ b/src/htmlparser/ElementNode.lua
@@ -1,5 +1,78 @@
 pcall(require, "luarocks.loader")
-local Set = require("Set")
+local Set = {}
+Set.mt = {__index = Set}
+function Set:new(values)
+  local instance = {}
+  local isSet if getmetatable(values) == Set.mt then isSet = true end
+  if type(values) == "table" then
+    if not isSet and #values > 0 then
+      for _,v in ipairs(values) do
+        instance[v] = true
+      end
+    else
+      for k in pairs(values) do
+        instance[k] = true
+      end
+    end
+  elseif values ~= nil then
+    instance = {[values] = true}
+  end
+  return setmetatable(instance, Set.mt)
+end
+
+function Set:add(e)
+  if e ~= nil then self[e] = true end
+  return self
+end
+
+function Set:remove(e)
+  if e ~= nil then self[e] = nil end
+  return self
+end
+
+function Set:tolist()
+  local res = {}
+  for k in pairs(self) do
+    table.insert(res, k)
+  end
+  return res
+end
+
+Set.mt.__add = function (a, b)
+  local res, a, b = Set:new(), Set:new(a), Set:new(b)
+  for k in pairs(a) do res[k] = true end
+  for k in pairs(b) do res[k] = true end
+  return res
+end
+
+-- Subtraction
+Set.mt.__sub = function (a, b)
+  local res, a, b = Set:new(), Set:new(a), Set:new(b)
+  for k in pairs(a) do res[k] = true end
+  for k in pairs(b) do res[k] = nil end
+  return res
+end
+
+-- Intersection
+Set.mt.__mul = function (a, b)
+  local res, a, b = Set:new(), Set:new(a), Set:new(b)
+  for k in pairs(a) do
+    res[k] = b[k]
+  end
+  return res
+end
+
+-- String representation
+Set.mt.__tostring = function (set)
+  local s = "{"
+  local sep = ""
+  for k in pairs(set) do
+    s = s .. sep .. tostring(k)
+    sep = ", "
+  end
+  return s .. "}"
+end
+
 
 local ElementNode = {}
 ElementNode.mt = {__index = ElementNode}