fixup: \libconcept marker

Author: jensmaurer

source/ranges.tex

@@ -1346,6 +1346,7 @@
 \end{itemdecl}
 
 \begin{itemdescr}
+\pnum
 For a type \tcode{R},
 \tcode{\exposid{is-initializer-list}<R>} is \tcode{true} if and only if
 \tcode{remove_cvref_t<R>} is a specialization of \tcode{initializer_list}.
@@ -3375,7 +3376,7 @@
   private:
     R @\exposid{r_}@ = R();         // \expos
   public:
-    owning_view() requires default_initializable<R> = default;
+    owning_view() requires @\libconcept{default_initializable}@<R> = default;
     constexpr owning_view(R&& t);
 
     owning_view(owning_view&&) = default;