P3050R2 Fix C++26 by optimizing linalg::conjugated for noncomplex value types

Editorial notes:
 * The editing instructions in the paper are rather unclear. We have
   applied the wording of the paper and replaced the original wording
   entirely, since the paper does not indicate deletions and
   insertions. Future versions of this draft may start rejecting
   instructions of such deficiency.
 * The leading words "the value" have been inserted in a "Returns:"
   element consisting of a list where the list items would otherwise
   have started with a codeblock (which does not get formatted
   correctly).
 * The feature test macro value is bumpted to 202412, since the
   previous motion (P3222R0) already uses 202411.

Author: tkoeppe

source/numerics.tex

@@ -12808,21 +12808,40 @@
 \begin{itemdescr}
 \pnum
 Let \tcode{A} be
+\begin{itemize}
+\item
 \tcode{remove_cvref_t<decltype(a.accessor().nested_accessor())>}
-if \tcode{Accessor} is a specialization of \tcode{conjugated_accessor}, and
-otherwise \tcode{conjugated_accessor<Accessor>}.
+if \tcode{Accessor} is a specialization of \tcode{conjugated_accessor}; otherwise,
+\item
+\tcode{Accessor} if \tcode{remove_cvref_t<ElementType>} is an arithmetic type; otherwise,
+\item
+\tcode{Accessor} if the expression \tcode{conj(E)} is not valid for any subexpression \tcode{E}
+whose type \tcode{T} is expression-equivalent to \tcode{remove_cvref_t<ElementType>}
+with overload resolution performed in a context that includes the declaration
+\tcode{template<class T> conj(const T\&) = delete;}; and otherwise,
+\item
+\tcode{conjugated_accessor<Accessor>}.
+\end{itemize}
 
 \pnum
 \returns
 \begin{itemize}
 \item
-If \tcode{Accessor} is a specialization of \tcode{conjugated_accessor},
+The value
 \begin{codeblock}
 mdspan<typename A::element_type, Extents, Layout, A>(a.data_handle(), a.mapping(),
                                                      a.accessor().nested_accessor())
 \end{codeblock}
+if \tcode{Accessor} is a specialization of \tcode{conjugated_accessor}; otherwise,
 \item
-otherwise,
+\tcode{a} if \tcode{remove_cvref_t<ElementType>} is an arithmetic type; otherwise,
+\item
+\tcode{a} if the expression \tcode{conj(E)} is not valid for any subexpression \tcode{E}
+whose type \tcode{T} is expression-equivalent to \tcode{remove_cvref_t<ElementType>}
+with overload resolution performed in a context that includes the declaration
+\tcode{template<class T> conj(const T\&) = delete;}; and otherwise,
+\item
+the value
 \begin{codeblock}
 mdspan<typename A::element_type, Extents, Layout, A>(a.data_handle(), a.mapping(),
                                                      conjugated_accessor(a.accessor()))

source/support.tex

@@ -710,7 +710,7 @@
 #define @\defnlibxname{cpp_lib_jthread}@                           201911L // also in \libheader{stop_token}, \libheader{thread}
 #define @\defnlibxname{cpp_lib_latch}@                             201907L // also in \libheader{latch}
 #define @\defnlibxname{cpp_lib_launder}@                           201606L // freestanding, also in \libheader{new}
-#define @\defnlibxname{cpp_lib_linalg}@                            202411L // also in \libheader{linalg}
+#define @\defnlibxname{cpp_lib_linalg}@                            202412L // also in \libheader{linalg}
 #define @\defnlibxname{cpp_lib_list_remove_return_type}@           201806L // also in \libheader{forward_list}, \libheader{list}
 #define @\defnlibxname{cpp_lib_logical_traits}@                    201510L // freestanding, also in \libheader{type_traits}
 #define @\defnlibxname{cpp_lib_make_from_tuple}@                   201606L // freestanding, also in \libheader{tuple}