diff --git a/lib/dummy.cpp b/lib/dummy.cpp
deleted file mode 100644
index 738e51c..0000000
--- a/lib/dummy.cpp
+++ /dev/null
@@ -1,2 +0,0 @@
-static int x=x;
-
diff --git a/lib/mealy.hpp b/lib/mealy.hpp
index 4f17dfb..df3385c 100644
--- a/lib/mealy.hpp
+++ b/lib/mealy.hpp
@@ -1,9 +1,15 @@
 #pragma once
 
+#include "phantom.hpp"
+
 #include <map>
 #include <string>
 #include <vector>
 
+using state = phantom<size_t, struct state_tag>;
+using input = phantom<size_t, struct input_tag>;
+using output = phantom<size_t, struct output_tag>;
+
 /*
  * Structure used for reading mealy files from dot files.
  * Everything is indexed by size_t's, so that we can index vectors
@@ -13,13 +19,13 @@
  */
 struct Mealy {
 	struct edge {
-		size_t to = -1;
-		size_t output = -1;
+		state to = -1;
+		output output = -1;
 	};
 
-	std::map<std::string, size_t> nodes_indices;
-	std::map<std::string, size_t> input_indices;
-	std::map<std::string, size_t> output_indices;
+	std::map<std::string, state> nodes_indices;
+	std::map<std::string, input> input_indices;
+	std::map<std::string, output> output_indices;
 
 	// state -> input -> (output, state)
 	std::vector<std::vector<edge>> graph;
@@ -31,19 +37,19 @@ struct Mealy {
 };
 
 inline auto is_complete(const Mealy & m){
-	for(int n = 0; n < m.graph_size; ++n){
-		if(m.graph[n].size() != m.input_size) return false;
-		for(auto && e : m.graph[n]) if(e.to == -1 || e.output == -1) return false;
+	for(state n = 0; n < m.graph_size; ++n){
+		if(m.graph[n.base()].size() != m.input_size) return false;
+		for(auto && e : m.graph[n.base()]) if(e.to == -1 || e.output == -1) return false;
 	}
 	return true;
 }
 
-inline auto apply(Mealy const & m, size_t state, size_t input){
-	return m.graph[state][input];
+inline auto apply(Mealy const & m, state state, input input){
+	return m.graph[state.base()][input.base()];
 }
 
 template <typename Iterator>
-auto apply(Mealy const & m, size_t state, Iterator b, Iterator e){
+auto apply(Mealy const & m, state state, Iterator b, Iterator e){
 	Mealy::edge ret;
 	while(b != e){
 		ret = apply(m, state, *b++);
diff --git a/lib/phantom.hpp b/lib/phantom.hpp
index e03b80f..07687b5 100644
--- a/lib/phantom.hpp
+++ b/lib/phantom.hpp
@@ -5,7 +5,13 @@
 
 template <typename Base, typename T>
 struct phantom : boost::operators<phantom<Base, T>>, boost::shiftable<phantom<Base, T>> {
+	phantom() = default;
 	phantom(Base y) : x(y) {}
+	phantom(phantom const &) = default;
+	phantom& operator=(phantom const &) = default;
+	phantom(phantom &&) = default;
+	phantom& operator=(phantom &&) = default;
+
 	explicit operator Base() const { return x; }
 	Base base() const { return x; }
 
@@ -41,4 +47,3 @@ std::ostream & operator<<(std::ostream & out, phantom<B, T> p){ return out << p.
 
 template <typename B, typename T>
 std::istream & operator>>(std::istream & in, phantom<B, T> & p){ return in >> p.x; }
-
diff --git a/lib/read_mealy_from_dot.cpp b/lib/read_mealy_from_dot.cpp
index 9e33a14..84b27ac 100644
--- a/lib/read_mealy_from_dot.cpp
+++ b/lib/read_mealy_from_dot.cpp
@@ -55,9 +55,9 @@ Mealy read_mealy_from_dot(istream& in, int verbose){
 
 		// add edge
 		m.graph.resize(m.graph_size);
-		auto & v = m.graph[m.nodes_indices[lh]];
+		auto & v = m.graph[m.nodes_indices[lh].base()];
 		v.resize(m.input_size);
-		v[m.input_indices[input]] = {m.nodes_indices[rh], m.output_indices[output]};
+		v[m.input_indices[input].base()] = {m.nodes_indices[rh], m.output_indices[output]};
 	}
 
 	if(verbose >= 1){
diff --git a/src/main.cpp b/src/main.cpp
index ded2abb..677f4a5 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -19,9 +19,9 @@ struct splijtboom {
 		iota(begin(states), end(states), 0);
 	}
 
-	vector<size_t> states;
+	vector<state> states;
 	vector<splijtboom> children;
-	vector<size_t> seperator;
+	vector<input> seperator;
 	int mark = 0;
 };
 
@@ -95,9 +95,9 @@ int main(int argc, char *argv[]){
 		}
 
 		// First try to split on output
-		for(size_t symbol = 0; symbol < P; ++symbol){
-			auto new_blocks = part.refine(block, [symbol, &g](size_t state){
-				return apply(g, state, symbol).output;
+		for(input symbol = 0; symbol < P; ++symbol){
+			auto new_blocks = part.refine(block, [symbol, &g](state state){
+				return apply(g, state, symbol).output.base();
 			}, Q);
 
 			if(elems_in(new_blocks) == 1){
@@ -129,14 +129,14 @@ int main(int argc, char *argv[]){
 		}
 
 		// Then try to split on state
-		for(size_t symbol = 0; symbol < P; ++symbol){
+		for(input symbol = 0; symbol < P; ++symbol){
 			vector<bool> successor_states(N, false);
 			for(auto && state : *block){
-				successor_states[g.graph[state][symbol].to] = true;
+				successor_states[apply(g, state, symbol).to.base()] = true;
 			}
 
-			auto & oboom = lca(root, [&successor_states](size_t state) -> bool{
-				return successor_states[state];
+			auto & oboom = lca(root, [&successor_states](state state) -> bool{
+				return successor_states[state.base()];
 			});
 
 			if(oboom.children.empty()){
@@ -163,7 +163,7 @@ int main(int argc, char *argv[]){
 			copy(begin(oboom.seperator), end(oboom.seperator), it);
 
 			auto new_blocks = part.refine(block, [&boom, &g](size_t state){
-				return apply(g, state, begin(boom.seperator), end(boom.seperator)).output;
+				return apply(g, state, begin(boom.seperator), end(boom.seperator)).output.base();
 			}, Q);
 
 			if(elems_in(new_blocks) == 1){