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diff --git a/libstdc++-v3/testsuite/24_iterators/indirect_callable/projected-adl.cc b/libstdc++-v3/testsuite/24_iterators/indirect_callable/projected-adl.cc
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+++ b/libstdc++-v3/testsuite/24_iterators/indirect_callable/projected-adl.cc
@@ -0,0 +1,42 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+
+// P2538R1 ADL-proof std::projected
+// https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2538r1.html
+
+#include <iterator>
+
+template<typename T>
+  concept has_diff_type = requires { typename T::difference_type; };
+
+static_assert( has_diff_type<std::projected<int*, void(*)(int)>> );
+
+struct Indy {
+  using value_type = int;
+  int operator*() const { return 0; }
+};
+static_assert( ! std::weakly_incrementable<Indy> );
+static_assert( ! has_diff_type<std::projected<Indy, void(*)(int)>> );
+
+
+// Examples from the paper:
+
+template<class T> struct Holder { T t; };
+struct Incomplete;
+
+void test_concepts()
+{
+  using T = Holder<Incomplete>*;
+  static_assert(std::equality_comparable<T>);
+  (void) std::indirectly_comparable<T*, T*, std::equal_to<>>;
+  (void) std::sortable<T*>;
+}
+
+#include <algorithm>
+
+void test_count()
+{
+  Holder<Incomplete>* a = nullptr;
+  (void) std::count(&a, &a, nullptr);
+  (void) std::ranges::count(&a, &a, nullptr); // { dg-bogus "." }
+}