--- a/util/set.lua	Mon Aug 10 22:16:05 2015 +0200
+++ b/util/set.lua	Sat Feb 21 10:36:37 2015 +0100
@@ -10,59 +10,19 @@
       ipairs, pairs, setmetatable, next, tostring;
 local t_concat = table.concat;
 
-module "set"
+local _ENV = nil;
 
 local set_mt = {};
 function set_mt.__call(set, _, k)
 	return next(set._items, k);
 end
-function set_mt.__add(set1, set2)
-	return _M.union(set1, set2);
-end
-function set_mt.__sub(set1, set2)
-	return _M.difference(set1, set2);
-end
-function set_mt.__div(set, func)
-	local new_set = _M.new();
-	local items, new_items = set._items, new_set._items;
-	for item in pairs(items) do
-		local new_item = func(item);
-		if new_item ~= nil then
-			new_items[new_item] = true;
-		end
-	end
-	return new_set;
-end
-function set_mt.__eq(set1, set2)
-	set1, set2 = set1._items, set2._items;
-	for item in pairs(set1) do
-		if not set2[item] then
-			return false;
-		end
-	end
-
-	for item in pairs(set2) do
-		if not set1[item] then
-			return false;
-		end
-	end
-
-	return true;
-end
-function set_mt.__tostring(set)
-	local s, items = { }, set._items;
-	for item in pairs(items) do
-		s[#s+1] = tostring(item);
-	end
-	return t_concat(s, ", ");
-end
 
 local items_mt = {};
 function items_mt.__call(items, _, k)
 	return next(items, k);
 end
 
-function new(list)
+local function new(list)
 	local items = setmetatable({}, items_mt);
 	local set = { _items = items };
 
@@ -116,7 +76,7 @@
 	return setmetatable(set, set_mt);
 end
 
-function union(set1, set2)
+local function union(set1, set2)
 	local set = new();
 	local items = set._items;
 
@@ -131,7 +91,7 @@
 	return set;
 end
 
-function difference(set1, set2)
+local function difference(set1, set2)
 	local set = new();
 	local items = set._items;
 
@@ -142,7 +102,7 @@
 	return set;
 end
 
-function intersection(set1, set2)
+local function intersection(set1, set2)
 	local set = new();
 	local items = set._items;
 
@@ -155,8 +115,55 @@
 	return set;
 end
 
-function xor(set1, set2)
+local function xor(set1, set2)
 	return union(set1, set2) - intersection(set1, set2);
 end
 
-return _M;
+function set_mt.__add(set1, set2)
+	return union(set1, set2);
+end
+function set_mt.__sub(set1, set2)
+	return difference(set1, set2);
+end
+function set_mt.__div(set, func)
+	local new_set = new();
+	local items, new_items = set._items, new_set._items;
+	for item in pairs(items) do
+		local new_item = func(item);
+		if new_item ~= nil then
+			new_items[new_item] = true;
+		end
+	end
+	return new_set;
+end
+function set_mt.__eq(set1, set2)
+	set1, set2 = set1._items, set2._items;
+	for item in pairs(set1) do
+		if not set2[item] then
+			return false;
+		end
+	end
+
+	for item in pairs(set2) do
+		if not set1[item] then
+			return false;
+		end
+	end
+
+	return true;
+end
+function set_mt.__tostring(set)
+	local s, items = { }, set._items;
+	for item in pairs(items) do
+		s[#s+1] = tostring(item);
+	end
+	return t_concat(s, ", ");
+end
+
+return {
+	new = new;
+	union = union;
+	difference = difference;
+	intersection = intersection;
+	xor = xor;
+};