diff --git a/lib/partition.hpp b/lib/partition.hpp
index bf049a6..1ae40af 100644
--- a/lib/partition.hpp
+++ b/lib/partition.hpp
@@ -8,81 +8,94 @@
 
 #include <iostream>
 
-namespace std {
-	template <typename Iterator>
-	auto begin(pair<Iterator, Iterator> p) { return p.first; }
-	template <typename Iterator>
-	auto end(pair<Iterator, Iterator> p) { return ++p.second; } // Kind of stupid
-}
+using Elements = std::list<size_t>;
 
-template <typename R>
-size_t elems_in(R range){
-	size_t ret = 0;
+struct Block {
+	Elements::iterator first;
+	Elements::iterator second;
 
-	auto b = range.first;
-	auto e = range.second;
-	while(b++ != e) ret++;
-	return ret;
-}
+	auto begin() const { return first; }
+	auto end() const { return std::next(second); }
+
+	bool operator==(Block const & rh) const {
+		return first == rh.first && second == rh.second;
+	}
+};
 
 struct partition_refine {
-	using Elements = std::list<size_t>;
-	using Block = std::pair<Elements::iterator, Elements::iterator>;
 	using Blocks = std::list<Block>;
 	using BlockRef = Blocks::iterator;
 
 	partition_refine(size_t n)
 	: elements(n, 0)
-	, blocks{{begin(elements), --end(elements)}}
-	, find_table(n, begin(blocks))
+	, blocks{{elements.begin(), --elements.end()}}
 	{
-		std::iota(begin(elements), end(elements), 0);
+		std::iota(elements.begin(), elements.end(), 0);
 	}
 
-	auto find(size_t element){
-		return find_table[element];
-	}
+	partition_refine(Block b)
+	: elements(b.begin(), b.end())
+	, blocks{{elements.begin(), --elements.end()}}
+	{}
 
-	auto size() const {
-		return blocks.size();
+	partition_refine() = delete;
+	partition_refine(partition_refine const &) = delete;
+	partition_refine& operator=(partition_refine const &) = delete;
+	partition_refine(partition_refine&&) = default;
+	partition_refine& operator=(partition_refine&&) = default;
+
+	auto size() const { return blocks.size(); }
+	auto begin() { return blocks.begin(); }
+	auto end() { return blocks.end(); }
+
+	// Deprecated since there is no more O(1) lookup
+	auto find(size_t x){
+		for(auto & b : blocks){
+			auto it = std::find(b.begin(), b.end(), x);
+			if(it != b.begin()) return b;
+		}
+
+		return Block{};
 	}
 
 	template <typename F>
-	auto refine(BlockRef br, F && function, size_t output_size){
+	auto refine(Block br, F && function, size_t output_size){
 		static_assert(std::is_same<decltype(function(0)), size_t>::value, "Function should return size_t");
-		if(br == BlockRef{}) throw std::logic_error("Passing null ref");
-		if(br == blocks.end()) throw std::logic_error("Invalid block");
-		if(br->first == elements.end() || br->second == elements.end()) throw std::logic_error("Invalid block range");
+		if(br == Block{}) throw std::logic_error("Empty block range");
+		if(br.first == elements.end() || br.second == elements.end()) throw std::logic_error("Invalid block range");
+
+		Blocks new_blocks;
 		std::vector<BlockRef> A(output_size);
 
-		auto b = *br;
-		auto r1 = blocks.erase(br);
-		auto r2 = r1;
-
-		auto it = begin(b);
-		auto ed = end(b);
+		auto it = br.begin();
+		auto ed = br.end();
 		while(it != ed){
-			const auto x = *it;
-			const auto y = function(x);
+			const auto y = function(*it);
 			if(y >= output_size) throw std::runtime_error("Output is too big");
 
 			auto & ar = A[y];
 			if(ar == BlockRef{}){
-				r2 = ar = blocks.insert(r2, {it, it});
+				ar = new_blocks.insert(new_blocks.end(), {it, it});
 				it++;
 			} else {
 				auto current = it++;
 				elements.splice(++ar->second, elements, current);
 				*ar = {ar->first, current};
 			}
-			find_table[x] = ar;
 		}
 
-		return make_pair(r2, r1);
+		return new_blocks;
+	}
+
+	auto replace(BlockRef br, Blocks new_blocks){
+		const auto it = blocks.erase(br);
+		const auto b = new_blocks.begin();
+		const auto e = std::prev(new_blocks.end());
+		blocks.splice(it, new_blocks);
+		return make_pair(b, std::next(e));
 	}
 
 private:
 	Elements elements;
-	std::list<Block> blocks;
-	std::vector<BlockRef> find_table;
+	Blocks blocks;
 };
diff --git a/src/main.cpp b/src/main.cpp
index 70dc271..8106e29 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -4,11 +4,12 @@
 #include <splitting_tree.hpp>
 #include <write_splitting_tree_to_dot.hpp>
 
+#include <algorithm>
 #include <cassert>
-#include <numeric>
+#include <iostream>
+#include <iterator>
 #include <queue>
-#include <type_traits>
-#include <vector>
+#include <utility>
 
 using namespace std;
 
@@ -39,10 +40,41 @@ int main(int argc, char *argv[]){
 	cout << "starting with " << part.size() << " blocks / " << N << " states" << endl;
 
 	queue<pair<partition_refine::BlockRef, reference_wrapper<splijtboom>>> work;
-	const auto push = [&work](auto br, auto & sp){ work.push({br, sp}); };
-	const auto pop = [&work](){ const auto r = work.front(); work.pop(); return r; };
+	const auto push = [&work](auto br, auto & sp) { work.push({br, sp}); };
+	const auto pop = [&work]() { const auto r = work.front(); work.pop(); return r; };
+	const auto add_push_new_block = [&](auto new_blocks, auto & boom) {
+		const auto nb = distance(new_blocks.first, new_blocks.second);
+		boom.children.assign(nb, splijtboom(0));
 
-	push(part.find(0), root);
+		auto i = 0;
+		while(new_blocks.first != new_blocks.second){
+			for(auto && s : *new_blocks.first){
+				boom.children[i].states.push_back(s);
+			}
+
+			push(new_blocks.first++, boom.children[i++]);
+		}
+
+		if(verbose){
+			cout << "splitted output into " << nb << endl;
+		}
+	};
+	const auto is_valid = [N, &g](auto blocks, auto symbol){
+		for(auto && block : blocks) {
+			partition_refine s_part(block);
+			const auto new_blocks = s_part.refine(*s_part.begin(), [symbol, &g](state state){
+				return apply(g, state, symbol).to.base();
+			}, N);
+			for(auto && new_block : new_blocks){
+				if(distance(new_block.begin(), new_block.end()) != 1) return false;
+			}
+		}
+		return true;
+	};
+
+	push(part.begin(), root);
+
+	size_t days_without_progress = 0;
 
 	while(!work.empty()){
 		auto block_boom = pop();
@@ -56,42 +88,23 @@ int main(int argc, char *argv[]){
 		}
 
 		if(boom.states.size() == 1) continue;
-		// if(elems_in(*block) == 1) continue;
-
-		if(verbose){
-			cout << "considering" << endl;
-		}
 
 		// First try to split on output
 		for(input symbol = 0; symbol < P; ++symbol){
-			auto new_blocks = part.refine(block, [symbol, &g](state state){
+			const auto new_blocks = part.refine(*block, [symbol, &g](state state){
 				return apply(g, state, symbol).output.base();
 			}, Q);
 
-			if(elems_in(new_blocks) == 1){
-				// continue with other input symbols
-				// (refine always updates the block)
-				block = new_blocks.first;
-				continue;
-			}
+			// no split -> continue with other input symbols
+			if(new_blocks.size() == 1) continue;
 
-			// a succesful split, add the children
-			const auto nb = distance(new_blocks.first, new_blocks.second);
-			boom.children.assign(nb, splijtboom(0));
+			// not a valid split -> continue
+			if(!is_valid(new_blocks, symbol)) continue;
+
+			// a succesful split, update partition and add the children
 			boom.seperator = {symbol};
-
-			auto i = 0;
-			while(new_blocks.first != new_blocks.second){
-				for(auto && s : *new_blocks.first){
-					boom.children[i].states.push_back(s);
-				}
-
-				push(new_blocks.first++, boom.children[i++]);
-			}
-
-			if(verbose){
-				cout << "splitted output into " << nb << endl;
-			}
+			const auto range = part.replace(block, move(new_blocks));
+			add_push_new_block(range, boom);
 
 			goto has_split;
 		}
@@ -107,61 +120,42 @@ int main(int argc, char *argv[]){
 				return successor_states[state.base()];
 			});
 
-			if(oboom.children.empty()){
-				// a leaf, hence not a split, try other symbols
+			// a leaf, hence not a split -> try other symbols
+			if(oboom.children.empty()) continue;
+
+			// possibly a succesful split, construct the children
+			const auto word = concat({symbol}, oboom.seperator);
+			const auto new_blocks = part.refine(*block, [word, &g](size_t state){
+				return apply(g, state, begin(word), end(word)).output.base();
+			}, Q);
+
+			// not a valid split -> continue
+			if(!is_valid(new_blocks, symbol)) continue;
+
+			if(new_blocks.size() == 1){
+				cerr << "WARNING: Refinement did not give finer partition, can not happen\n";
 				continue;
 			}
 
-			if(verbose){
-				cout << "split\t";
-				for(auto s : oboom.states) cout << s << " ";
-				cout << endl;
-				cout << "into ";
-				for(auto & c : oboom.children) {
-					for(auto s : c.states) cout << s << " ";
-					cout << "- ";
-				}
-				cout << endl;
-			}
-
-			// a succesful split, construct the children
-			boom.seperator.resize(oboom.seperator.size() + 1);
-			auto it = begin(boom.seperator);
-			*it++ = symbol;
-			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.base();
-			}, Q);
-
-			if(elems_in(new_blocks) == 1){
-				throw logic_error("Refinement did not give finer partition, can not happen");
-			}
-
-			const auto nb = distance(new_blocks.first, new_blocks.second);
-			boom.children.assign(nb, splijtboom(0));
-
-			auto i = 0;
-			while(new_blocks.first != new_blocks.second){
-				for(auto && s : *new_blocks.first){
-					boom.children[i].states.push_back(s);
-				}
-
-				push(new_blocks.first++, boom.children[i++]);
-			}
-
-			if(verbose){
-				cout << "splitted state into " << nb << endl;
-			}
+			// update partition and add the children
+			boom.seperator = word;
+			const auto range = part.replace(block, move(new_blocks));
+			add_push_new_block(range, boom);
 
 			goto has_split;
 		}
-		push(block, boom);
+
 		cout << "no split :(" << endl;
+		if(days_without_progress++ >= work.size()) {
+			cerr << "No distinguishing seq found!\n";
+			break;
+		}
+		push(block, boom);
+		continue;
 
 		has_split:
-		cout << "we have " << part.size() << " blocks / " << N << " states" << endl;
-		cout << "and still " << work.size() << " work" << endl;
+		cout << "blocks: " << part.size() << ", states: " << N << ", work: " << work.size() << endl;
+		days_without_progress = 0;
 	}
 
 	write_splitting_tree_to_dot(root, filename + ".splitting_tree.dot");
diff --git a/src/partition_test.cpp b/src/partition_test.cpp
index a108e95..928dd55 100644
--- a/src/partition_test.cpp
+++ b/src/partition_test.cpp
@@ -8,23 +8,23 @@ int main(int argc, char *argv[]){
 	partition_refine p(50);
 
 	auto bs = p.refine(p.find(0), [](size_t x){ return x % 1; }, 1);
-	cout << elems_in(bs) << endl;
+	cout << bs.size() << endl;
 
 	bs = p.refine(p.find(0), [](size_t x){ return x % 2; }, 2);
-	cout << elems_in(bs) << endl;
+	cout << bs.size() << endl;
 
 	bs = p.refine(p.find(0), [](size_t x){ return x % 3; }, 3);
-	cout << elems_in(bs) << endl;
+	cout << bs.size() << endl;
 
 	bs = p.refine(p.find(0), [](size_t x){ return x % 5; }, 5);
-	cout << elems_in(bs) << endl;
+	cout << bs.size() << endl;
 
 	bs = p.refine(p.find(0), [](size_t x){ return x % 7; }, 7);
-	cout << elems_in(bs) << endl;
+	cout << bs.size() << endl;
 
 	for(int i = 0; i < 50; ++i){
 		cout << i << ":\t";
-		const auto block = *p.find(i);
+		const auto block = p.find(i);
 		for(auto && x : block) cout << x << " ";
 		cout << endl;
 	}