diff --git a/include/clusters.hpp b/include/clusters.hpp
index 4e98e42..5d9feda 100644
--- a/include/clusters.hpp
+++ b/include/clusters.hpp
@@ -16,42 +16,39 @@ auto make_empty(Field field, Cluster const & c){
 }
 
 namespace detail {
-	template <typename Field>
-	auto same_group(Field const & field, typename Field::Position const & p, typename Field::Position const & q){
-		return field.get(p) == field.get(q);
-	}
-
-	template <typename Field>
-	void cluster_expand(Field const & field, typename Field::Position const & p, boost::container::flat_set<typename Field::Position>& ret){
+	template <typename Field, typename Rules>
+	void cluster_expand(Field const & field, Rules const & rules, typename Field::Position const & p, boost::container::flat_set<typename Field::Position>& ret){
 		for(auto&& q : field.neighbors(p)){
-			if(!same_group(field, p, q)) continue;
+			if(!rules.same_cluster(field.get(p), field.get(q))) continue;
 
 			if(ret.insert(q).second){
-				cluster_expand(field, q, ret);
+				cluster_expand(field, rules, q, ret);
 			}
 		}
 	}
 }
 
-template <typename Field>
-auto cluster_at(Field const & field, typename Field::Position const & p){
+template <typename Field, typename Rules>
+auto cluster_at(Field const & field, Rules const & rules, typename Field::Position const & p){
 	boost::container::flat_set<typename Field::Position> ret;
 	ret.reserve(10); // speed improvement of 20%
 	ret.insert(p);
-	detail::cluster_expand(field, p, ret);
+	detail::cluster_expand(field, rules, p, ret);
 	return ret;
 }
 
 template <typename Grid, typename Rules>
 auto all_clusters(Grid const & grid, Rules const & rules){
-	std::vector<decltype(cluster_at(grid, std::declval<typename Grid::Position>()))> ret;
+	std::vector<decltype(cluster_at(grid, rules, std::declval<typename Grid::Position>()))> ret;
 	ret.reserve(10);
+
 	auto partition = make_empty(grid, grid.all_positions());
 	auto current_p = 1;
 	for(auto&& p : partition.all_positions()){
+		// ignore if it already belongs to a cluster or is empty
 		if(!partition.empty(p) || grid.empty(p)) continue;
 
-		auto cluster = cluster_at(grid, p);
+		auto cluster = cluster_at(grid, rules, p);
 		for(auto&& q : cluster){
 			partition.get(q) = current_p;
 		}
diff --git a/include/rules.hpp b/include/rules.hpp
index bf577c9..b46797d 100644
--- a/include/rules.hpp
+++ b/include/rules.hpp
@@ -9,6 +9,10 @@ struct BasicRules {
 		return min_size;
 	}
 
+	auto same_cluster(int x, int y) const {
+		return x == y;
+	}
+
 private:
 	unsigned int min_size;
 };