diff --git a/init.lua b/init.lua
index 5fa6e6c..1e24c42 100644
--- a/init.lua
+++ b/init.lua
@@ -13,23 +13,24 @@ local mon_meta = {}
 mon_meta.__index = mon_meta
 
 -- A monoid object is a table with the following fields:
+--   def: The monoid definition
 --   player_map: A map from player names to their effect tables. Effect tables
 --     are maps from effect IDs to values.
 --   value_cache: A map from player names to the cached value for the monoid.
 --   next_id: The next unique ID to assign an effect.
 
 local function monoid(def)
-        local mon = {}
+	local mon = {}
 
 	local p_map = {}
         mon.player_map = p_map
 
-        mon.next_id = 1
+	mon.next_id = 1
 
 	local v_cache = {}
 	mon.value_cache = v_cache
 
-        setmetatable(mon, mon_methods)
+	setmetatable(mon, mon_methods)
 
 	minetest.register_on_leaveplayer(function(player)
 		local p_name = player:get_player_name()
@@ -37,54 +38,56 @@ local function monoid(def)
 		v_cache[p_name] = nil
 	end)
 
-        return mon
+	return mon
 end
 
 player_monoids.make_monoid = monoid
 
 function mon_meta:add_change(player, value)
-        local p_name = player:get_player_name()
+	local p_name = player:get_player_name()
+
+	local def = self.def
         
-        local p_effects = self.player_map[p_name]
-        if p_effects == nil then
-                p_effects = {}
-                self.player_map[p_name] = p_effects
-        end
+	local p_effects = self.player_map[p_name]
+	if p_effects == nil then
+		p_effects = {}
+		self.player_map[p_name] = p_effects
+	end
 
-        local actual_id
+	local actual_id
 
-        if id then
-                actual_id = id
-        else
-                actual_id = self.next_id
-                self.next_id = actual_id + 1
-        end
+	if id then
+		actual_id = id
+	else
+		actual_id = self.next_id
+		self.next_id = actual_id + 1
+	end
 
-        local old_total = self.value_cache[p_name]
-        p_effects[actual_id] = value
-	local new_total = self.fold(p_effects)
-        self.value_cache[p_name] = new_total
+	local old_total = self.value_cache[p_name]
+	p_effects[actual_id] = value
+	local new_total = def.fold(p_effects)
+	self.value_cache[p_name] = new_total
         
-        self.apply(new_total, player)
-        self.on_change(old_total, new_total, player)
+	def.apply(new_total, player)
+	def.on_change(old_total, new_total, player)
 end
 
 function mon_meta:del_change(player, id)
-        local p_name = player:get_player_name()
+	local p_name = player:get_player_name()
 
-        local p_effects = self.player_map[p_name]
-        if p_effects == nil then return end
+	local p_effects = self.player_map[p_name]
+	if p_effects == nil then return end
 
-        local old_total = self.value_cache[p_name]
-        p_effects[id] = nil
-        local new_total = self.fold(p_effects)
-        self.value_cache[p_name] = new_total
+	local old_total = self.value_cache[p_name]
+	p_effects[id] = nil
+	local new_total = def.fold(p_effects)
+	self.value_cache[p_name] = new_total
 
-        self.apply(new_total, player)
-        self.on_change(old_total, new_total, player)
+	def.apply(new_total, player)
+	def.on_change(old_total, new_total, player)
 end
 
 function mon_meta:value(player)
-        local p_name = player:get_player_name()
-        return self.value_cache[p_name] or self.identity
+	local p_name = player:get_player_name()
+	return self.value_cache[p_name] or self.def.identity
 end