diff --git a/ac/c++-features.m4 b/ac/c++-features.m4
index c46c6b576..a8c3d39b1 100644
--- a/ac/c++-features.m4
+++ b/ac/c++-features.m4
@@ -4,7 +4,7 @@ AC_DEFUN([AX_CXX_STD_CXX_FLAG],[
     AC_LANG_PUSH(C++)
     CXXFLAGS_SAVED="$CXXFLAGS"
 
-    for flag in c++17 gnu++14 c++14 gnu++11 c++11 c++0x; do
+    for flag in c++17; do
       CXXFLAGS="$CXXFLAGS_SAVED -std=$flag"
       AC_TRY_COMPILE([], [true;], [ax_cv_std_cxx_flag="-std=$flag"], [ax_cv_std_cxx_flag="undecided"])
 
@@ -29,352 +29,6 @@ AC_DEFUN([AX_CXX_STD_CXX_FLAG],[
   AC_SUBST(STD_CXX)
 ])
 
-AC_DEFUN([AX_CXX11_INITIALIZER_LISTS],[
-  AC_CACHE_CHECK([for support for C++11 feature "initializer lists"], [ax_cv_cxx11_initializer_lists],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [
-#include <string>
-#include <vector>
-],
-      [std::vector<std::string> listy = { "asd", "qwe", "123" };],
-      [ax_cv_cxx11_initializer_lists="yes"],
-      [ax_cv_cxx11_initializer_lists="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx11_initializer_lists" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * initializer lists (C++11)"
-  fi
-])
-
-AC_DEFUN([AX_CXX11_RANGE_BASED_FOR],[
-  AC_CACHE_CHECK([for support for C++11 feature "range-based 'for'"], [ax_cv_cxx11_range_based_for],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [
-#include <string>
-#include <vector>
-],[
-std::string total;
-std::vector<std::string> listy = { "asd", "qwe", "123" };
-for (std::string &s : listy)
-  total += s;
-],
-      [ax_cv_cxx11_range_based_for="yes"],
-      [ax_cv_cxx11_range_based_for="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx11_range_based_for" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * range-based 'for' (C++11)"
-  fi
-])
-
-AC_DEFUN([AX_CXX11_RIGHT_ANGLE_BRACKETS],[
-  AC_CACHE_CHECK([for support for C++11 feature "right angle brackets"], [ax_cv_cxx11_right_angle_brackets],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [
-#include <map>
-#include <vector>
-
-typedef std::map<int, std::vector<int>> unicorn;
-],
-      [unicorn charlie;],
-      [ax_cv_cxx11_right_angle_brackets="yes"],
-      [ax_cv_cxx11_right_angle_brackets="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx11_right_angle_brackets" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * right angle brackets (C++11)"
-  fi
-])
-
-AC_DEFUN([AX_CXX11_AUTO_KEYWORD],[
-  AC_CACHE_CHECK([for support for C++11 feature "'auto' keyword"], [ax_cv_cxx11_auto_keyword],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [
-#include <vector>
-],[
-  std::vector<unsigned int> listy;
-  unsigned int sum = 0;
-  for (auto i = listy.begin(); i < listy.end(); i++)
-    sum += *i;
-],
-      [ax_cv_cxx11_auto_keyword="yes"],
-      [ax_cv_cxx11_auto_keyword="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx11_auto_keyword" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * 'auto' keyword (C++11)"
-  fi
-])
-
-AC_DEFUN([AX_CXX11_LAMBDA_FUNCTIONS],[
-  AC_CACHE_CHECK([for support for C++11 feature "lambda functions"], [ax_cv_cxx11_lambda_functions],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [
-#include <algorithm>
-#include <vector>
-],
-      [
-std::vector<unsigned int> listy;
-unsigned int sum = 0;
-std::for_each(listy.begin(), listy.end(), [&](unsigned int i) { sum += i; });
-],
-      [ax_cv_cxx11_lambda_functions="yes"],
-      [ax_cv_cxx11_lambda_functions="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx11_lambda_functions" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * lambda functions (C++11)"
-  fi
-])
-
-AC_DEFUN([AX_CXX11_NULLPTR],[
-  AC_CACHE_CHECK([for support for C++11 feature "nullptr"], [ax_cv_cxx11_nullptr],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [],
-      [unsigned char const *charlie = nullptr;],
-      [ax_cv_cxx11_nullptr="yes"],
-      [ax_cv_cxx11_nullptr="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx11_nullptr" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * nullptr (C++11)"
-  fi
-])
-
-AC_DEFUN([AX_CXX11_TUPLES],[
-  AC_CACHE_CHECK([for support for C++11 feature "tuples"], [ax_cv_cxx11_tuples],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [#include <tuple>],
-      [
-  std::tuple<int, int, char> t = std::make_tuple(1, 2, 'c');
-  std::get<2>(t) += std::get<0>(t) * std::get<1>(t);
-],
-      [ax_cv_cxx11_tuples="yes"],
-      [ax_cv_cxx11_tuples="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx11_tuples" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * tuples (C++11)"
-  fi
-])
-
-AC_DEFUN([AX_CXX11_ALIAS_DECLARATIONS],[
-  AC_CACHE_CHECK([for support for C++11 feature "alias declarations"], [ax_cv_cxx11_alias_declarations],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [
-#include <vector>
-using thingy = std::vector<int>;
-],[
-  thingy things;
-  things.push_back(42);
-],
-      [ax_cv_cxx11_alias_declarations="yes"],
-      [ax_cv_cxx11_alias_declarations="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx11_alias_declarations" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * alias declarations (C++11)"
-  fi
-])
-
-AC_DEFUN([AX_CXX14_MAKE_UNIQUE],[
-  AC_CACHE_CHECK([for support for C++14 feature "std::make_unique"], [ax_cv_cxx14_make_unique],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [#include <memory>],
-      [auto i_ptr{std::make_unique<int>(42)};],
-      [ax_cv_cxx14_make_unique="yes"],
-      [ax_cv_cxx14_make_unique="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx14_make_unique" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * std::make_unique function (C++14)"
-  fi
-])
-
-AC_DEFUN([AX_CXX14_DIGIT_SEPARATORS],[
-  AC_CACHE_CHECK([for support for C++14 feature "digit separators"], [ax_cv_cxx14_digit_separators],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [],
-      [auto num = 10'000'000'000ll;],
-      [ax_cv_cxx14_digit_separators="yes"],
-      [ax_cv_cxx14_digit_separators="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx14_digit_separators" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * digit separators (C++14)"
-  fi
-])
-
-AC_DEFUN([AX_CXX14_BINARY_LITERALS],[
-  AC_CACHE_CHECK([for support for C++14 feature "binary literals"], [ax_cv_cxx14_binary_literals],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [],
-      [auto num1 = 0b00101010;
-       auto num2 = 0B00101010;
-       auto num3 = 0b0010'1010;],
-      [ax_cv_cxx14_binary_literals="yes"],
-      [ax_cv_cxx14_binary_literals="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx14_binary_literals" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * binary literals (C++14)"
-  fi
-])
-
-AC_DEFUN([AX_CXX14_GENERIC_LAMBDAS],[
-  AC_CACHE_CHECK([for support for C++14 feature "generic lambdas"], [ax_cv_cxx14_generic_lambdas],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [
-        #include <algorithm>
-        #include <vector>
-      ],
-      [
-        std::vector<int> vv;
-        std::sort(vv.begin(), vv.end(), [](auto &a, auto &b) { return b < a; });
-      ],
-      [ax_cv_cxx14_generic_lambdas="yes"],
-      [ax_cv_cxx14_generic_lambdas="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx14_generic_lambdas" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * generic lambdas (C++14)"
-  fi
-])
-
-AC_DEFUN([AX_CXX14_USER_DEFINED_LITERALS_FOR_STD_STRING],[
-  AC_CACHE_CHECK([for support for C++14 feature "User-defined literals for std::string"], [ax_cv_cxx14_user_defined_literals_for_std_string],[
-
-    CXXFLAGS_SAVED=$CXXFLAGS
-    CXXFLAGS="$CXXFLAGS $STD_CXX"
-    export CXXFLAGS
-
-    AC_LANG_PUSH(C++)
-    AC_TRY_COMPILE(
-      [
-#include <string>
-using namespace std::string_literals;
-      ],
-      [return "hello"s.length();],
-      [ax_cv_cxx14_user_defined_literals_for_std_string="yes"],
-      [ax_cv_cxx14_user_defined_literals_for_std_string="no"])
-    AC_LANG_POP
-
-    CXXFLAGS="$CXXFLAGS_SAVED"
-  ])
-
-  if ! test x"$ax_cv_cxx14_user_defined_literals_for_std_string" = xyes ; then
-    missing_cxx_features="$missing_cxx_features\n  * User-defined literals for std::string (C++14)"
-  fi
-])
-
 AC_DEFUN([AX_CXX17_ATTRIBUTE_MAYBE_UNUSED],[
   AC_CACHE_CHECK([for support for C++17 feature "attribute 'maybe_unused'"], [ax_cv_cxx17_attribute_maybe_unused],[
 
@@ -553,19 +207,6 @@ dnl   fi
 dnl ])
 
 AX_CXX_STD_CXX_FLAG
-AX_CXX11_INITIALIZER_LISTS
-AX_CXX11_RANGE_BASED_FOR
-AX_CXX11_RIGHT_ANGLE_BRACKETS
-AX_CXX11_AUTO_KEYWORD
-AX_CXX11_LAMBDA_FUNCTIONS
-AX_CXX11_NULLPTR
-AX_CXX11_TUPLES
-AX_CXX11_ALIAS_DECLARATIONS
-AX_CXX14_MAKE_UNIQUE
-AX_CXX14_DIGIT_SEPARATORS
-AX_CXX14_BINARY_LITERALS
-AX_CXX14_GENERIC_LAMBDAS
-AX_CXX14_USER_DEFINED_LITERALS_FOR_STD_STRING
 AX_CXX17_ATTRIBUTE_MAYBE_UNUSED
 AX_CXX17_NESTED_NAMESPACE_DEFINITION
 AX_CXX17_STRUCTURED_BINDINGS
@@ -574,8 +215,8 @@ AX_CXX17_STD_GCD
 AX_CXX17_CONSTEXPR_IF
 
 if test x"$missing_cxx_features" != x ; then
-  printf "The following features of the C++11/C++14/C++17 standards are not supported by $CXX:$missing_cxx_features\n"
+  printf "The following features of the C++17 standards are not supported by $CXX:$missing_cxx_features\n"
   printf "If you are using the GNU C compiler collection (gcc), you need\n"
   printf "at least v7; for clang v4 and newer should work.\n"
-  AC_MSG_ERROR([support for required C++11/C++14/C++17 features incomplete])
+  AC_MSG_ERROR([support for required C++17 features incomplete])
 fi