diff --git a/include/duckhandy/sequence_bt.hpp b/include/duckhandy/sequence_bt.hpp
deleted file mode 100644
index ee92e92..0000000
--- a/include/duckhandy/sequence_bt.hpp
+++ /dev/null
@@ -1,54 +0,0 @@
-/* Copyright 2016-2021 Michele Santullo
- * This file is part of "duckhandy".
- *
- * "duckhandy" is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * "duckhandy" is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with "duckhandy".  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#ifndef id4FAEF395B9ED47CB9D6B50B54C9A289A
-#define id4FAEF395B9ED47CB9D6B50B54C9A289A
-
-#include <cstddef>
-
-namespace dhandy {
-	namespace bt {
-		template <typename T, T... I>
-		struct number_seq {
-		};
-
-		template <std::size_t... I>
-		using index_seq = number_seq<std::size_t, I...>;
-
-		namespace implem {
-			template <typename T, T MIN, T MAX, T... I>
-			struct range_builder;
-
-			template <typename T, T MIN, T... I>
-			struct range_builder<T, MIN, MIN, I...> {
-				typedef number_seq<T, I...> type;
-			};
-
-			template <typename T, T MIN, T N, T... I>
-			struct range_builder : public range_builder<T, MIN, N - 1, N - 1, I...> {
-			};
-		} //namespace implem
-
-		template <typename T, T MIN, T MAX>
-		using number_range = typename implem::range_builder<T, MIN, MAX>::type;
-
-		template <std::size_t MIN, std::size_t MAX>
-		using index_range = number_range<std::size_t, MIN, MAX>;
-	} //namespace bt
-} //namespace dhandy
-
-#endif
diff --git a/include/duckhandy/string_bt.hpp b/include/duckhandy/string_bt.hpp
index a7f1862..9d6cdb6 100644
--- a/include/duckhandy/string_bt.hpp
+++ b/include/duckhandy/string_bt.hpp
@@ -18,7 +18,7 @@
 #ifndef id170B0E6C34D14EBA9B92A35977BDBFB3
 #define id170B0E6C34D14EBA9B92A35977BDBFB3
 
-#include "sequence_bt.hpp"
+#include <utility>
 #include <cstddef>
 #include <iostream>
 #include <stdexcept>
@@ -58,7 +58,7 @@ namespace dhandy {
 
 		private:
 			template <std::size_t... I>
-			constexpr string ( const index_seq<I...>&, const value_type* parString );
+			constexpr string ( const std::index_sequence<I...>&, const value_type* parString );
 
 			const value_type m_data[S];
 		};
@@ -70,7 +70,7 @@ namespace dhandy {
 
 		namespace implem {
 			template <std::size_t S, std::size_t S2, std::size_t... I>
-			constexpr string<S + S2 - 1> concat ( const index_seq<I...>&, const string<S>& parLeft, const string<S2>& parRight ) {
+			constexpr string<S + S2 - 1> concat ( const std::index_sequence<I...>&, const string<S>& parLeft, const string<S2>& parRight ) {
 				return string<S + S2 - 1>(
 					(I < S - 1 ? parLeft[I] : (I < S + S2 - 2 ? parRight[I - (S - 1)] : '\0'))...
 				);
@@ -83,14 +83,14 @@ namespace dhandy {
 
 		template <std::size_t S, typename Ch>
 		template <std::size_t... I>
-		constexpr string<S, Ch>::string (const index_seq<I...>&, const value_type* parString) :
+		constexpr string<S, Ch>::string (const std::index_sequence<I...>&, const value_type* parString) :
 			m_data{parString[I]...}
 		{
 		}
 
 		template <std::size_t S, typename Ch>
 		inline constexpr string<S, Ch>::string (const value_type* parString) :
-			string(index_range<0, S>(), parString)
+			string(std::make_index_sequence<S>(), parString)
 		{
 		}
 
@@ -104,7 +104,7 @@ namespace dhandy {
 		template <std::size_t S, typename Ch>
 		template <std::size_t S2>
 		constexpr inline string<S + S2 - 1, Ch> string<S, Ch>::operator+ (const string<S2, Ch>& parOther) const {
-			return implem::concat(index_range<0, S + S2 - 1>(), string<S>(m_data), parOther);
+			return implem::concat(std::make_index_sequence<S + S2 - 1>(), string<S>(m_data), parOther);
 		}
 
 		template <std::size_t S, typename Ch>