](https://wg21.link/P2592R3)  
` __cpp_lib_chrono_udls ` |  [ User-defined literals for time types ](/w/cpp/chrono/duration#Literals "cpp/chrono/duration") |  201304L  |  [ ` <chrono> ` ](/w/cpp/header/chrono "cpp/header/chrono") |  (C++14)  |  [ N3642 ](https://wg21.link/N3642)  
` __cpp_lib_clamp ` |  [ std::clamp ](/w/cpp/algorithm/clamp "cpp/algorithm/clamp") |  201603L  |  [ ` <algorithm> ` ](/w/cpp/header/algorithm "cpp/header/algorithm") |  (C++17)  |  [ P0025R0 ](https://wg21.link/P0025R0)  
` __cpp_lib_common_reference ` |  Make  std::common_reference_t  of  [ std::reference_wrapper ](/w/cpp/utility/functional/reference_wrapper "cpp/utility/functional/reference wrapper") a reference type  |  202302L  |  [ ` <type_traits> ` ](/w/cpp/header/type_traits "cpp/header/type traits") |  (C++23)  |  [ P2655R3 ](https://wg21.link/P2655R3)  
` __cpp_lib_common_  reference_wrapper ` |  Make  std::common_reference_t  of  [ std::reference_wrapper ](/w/cpp/utility/functional/reference_wrapper "cpp/utility/functional/reference wrapper") a reference type  |  202302L  |  [ ` <functional> ` ](/w/cpp/header/functional "cpp/header/functional") |  (C++23)  |  [ P2655R3 ](https://wg21.link/P2655R3)  
` __cpp_lib_complex_udls ` |  [ User-defined Literals for ` std::complex ` ](/w/cpp/numeric/complex/operator%22%22i "cpp/numeric/complex/operator""i") |  201309L  |  [ ` <complex> ` ](/w/cpp/header/complex "cpp/header/complex") |  (C++14)  |  [ N3779 ](https://wg21.link/N3779)  
` __cpp_lib_concepts ` |  [ Standard library concepts ](/w/cpp/concepts "cpp/concepts") |  202002L  |  [ ` <concepts> ` ](/w/cpp/header/concepts "cpp/header/concepts") |  (C++20)  |  [ P0898R3 ](https://wg21.link/P0898R3)   
[ P1754R1 ](https://wg21.link/P1754R1)  
[ P1964R2 ](https://wg21.link/P1964R2)  
Move-only types for [ ` equality_comparable_with ` ](/w/cpp/concepts/equality_comparable "cpp/concepts/equality comparable") , [ ` totally_ordered_with ` ](/w/cpp/concepts/totally_ordered "cpp/concepts/totally ordered") , and [ ` three_way_comparable_with ` ](/w/cpp/utility/compare/three_way_comparable "cpp/utility/compare/three way comparable") |  202207L  |  [ ` <compare> ` ](/w/cpp/header/compare "cpp/header/compare") [ ` <concepts> ` ](/w/cpp/header/concepts "cpp/header/concepts") |  (C++23)  |  [ P2404R3 ](https://wg21.link/P2404R3)  
` __cpp_lib_constexpr_algorithms ` |  Constexpr for [ algorithms ](/w/cpp/algorithm "cpp/algorithm") |  201806L  |  [ ` <algorithm> ` ](/w/cpp/header/algorithm "cpp/header/algorithm") [ ` <utility> ` ](/w/cpp/header/utility "cpp/header/utility") |  (C++20)  |  [ P0202R3 ](https://wg21.link/P0202R3)   
[ P0879R0 ](https://wg21.link/P0879R0)  
[ LWG3256 ](https://wg21.link/LWG3256)  
[ LWG3792 ](https://wg21.link/LWG3792)  
Constexpr stable sorting  |  202306L  |  [ ` <algorithm> ` ](/w/cpp/header/algorithm "cpp/header/algorithm") [ ` <utility> ` ](/w/cpp/header/utility "cpp/header/utility") |  (C++26)  |  [ P2562R1 ](https://wg21.link/P2562R1)  
` __cpp_lib_constexpr_bitset ` |  A more constexpr  [ std::bitset ](/w/cpp/utility/bitset "cpp/utility/bitset") |  202207L  |  [ ` <bitset> ` ](/w/cpp/header/bitset "cpp/header/bitset") |  (C++23)  |  [ P2417R2 ](https://wg21.link/P2417R2)  
` __cpp_lib_constexpr_charconv ` |  Add ` constexpr ` modifiers to functions  std::to_chars  and  std::from_chars  for integral types  |  202207L  |  [ ` <charconv> ` ](/w/cpp/header/charconv "cpp/header/charconv") |  (C++23)  |  [ P2291R3 ](https://wg21.link/P2291R3)  
` __cpp_lib_constexpr_cmath ` |  Constexpr for mathematical functions in [ ` <cmath> ` ](/w/cpp/header/cmath "cpp/header/cmath") and [ ` <cstdlib> ` ](/w/cpp/header/cstdlib "cpp/header/cstdlib") |  202202L  |  [ ` <cmath> ` ](/w/cpp/header/cmath "cpp/header/cmath") [ ` <cstdlib> ` ](/w/cpp/header/cstdlib "cpp/header/cstdlib") |  (C++23)  |  [ P0533R9 ](https://wg21.link/P0533R9)  
More constexpr for [ ` <cmath> ` ](/w/cpp/header/cmath "cpp/header/cmath") |  202306L  |  [ ` <cmath> ` ](/w/c