fix some mistakes in wording

concat.md

@@ -750,7 +750,8 @@ namespace std::ranges {
 
     constexpr auto end() requires(!(@_simple-view_@<Views> && ...));
 
-    constexpr auto end() const requires(range<const Views>&&...);
+    constexpr auto end() const
+      requires((range<const Views> && ...) && @_concatable_@<const Views...>);
 
     constexpr auto size() requires(sized_range<Views>&&...);
 
@@ -823,7 +824,7 @@ concept @_concat-is-random-access_@ = @*see below*@; // exposition only
 
 :::bq
 
-[3]{.pnum} Let `Fs` be the pack that consists of all elements of `Rs` except the last, then `@_concat-is-random-access_@` is equivalent to:
+[3]{.pnum} Let `Fs` be the pack that consists of all elements of `Rs` except the last element, then `@_concat-is-random-access_@` is equivalent to:
 
 ```cpp
 template <bool Const, class... Rs>
@@ -882,7 +883,8 @@ return it;
 
 ```cpp
 constexpr auto end() requires(!(@_simple-view_@<Views> && ...));
-constexpr auto end() const requires(range<const Views>&&...);
+constexpr auto end() const
+  requires((range<const Views> && ...) && @_concatable_@<const Views...>);
 ```
 
 :::bq
@@ -1014,7 +1016,7 @@ namespace std::ranges{
 
     friend constexpr auto operator<=>(const @_iterator_@& x, const @_iterator_@& y)
         requires (@*all-random-access*@<Const, Views...> &&
-         (three_way_comparable<@_maybe-const_@<Const, Views>> &&...));
+         (three_way_comparable<iterator_t<@_maybe-const_@<Const, Views>>> && ...));
 
     friend constexpr @_iterator_@ operator+(const @_iterator_@& it, difference_type n)
         requires @_concat-is-random-access_@<Const, Views...>;
@@ -1185,7 +1187,7 @@ explicit constexpr @_iterator_@(
 ```cpp
 constexpr @_iterator_@(@_iterator_@<!Const> it) 
     requires Const &&
-    (convertible_to<iterator_t<Views>, iterator_t<const Views>>&&...);
+    (convertible_to<iterator_t<Views>, iterator_t<const Views>> && ...);
 ```
 
 :::bq
@@ -1398,7 +1400,7 @@ friend constexpr bool operator>=(const @_iterator_@& x, const @_iterator_@& y)
     requires @*all-random-access*@<Const, Views...>;
 friend constexpr auto operator<=>(const @_iterator_@& x, const @_iterator_@& y)
    requires (@*all-random-access*@<Const, Views...> &&
-    (three_way_comparable<@_maybe-const_@<Const, Views>> &&...));
+    (three_way_comparable<iterator_t<@_maybe-const_@<Const, Views>>> && ...));
 ```
 
 :::bq
@@ -1428,7 +1430,7 @@ friend constexpr @_iterator_@ operator+(const @_iterator_@& it, difference_type
 [30]{.pnum} *Effects*: Equivalent to:
 
 ```cpp
-return @_iterator_@{it} += n;
+return @_iterator_@(it) += n;
 ```
 
 :::
@@ -1458,7 +1460,7 @@ friend constexpr @_iterator_@ operator-(const @_iterator_@& it, difference_type
 [32]{.pnum} *Effects*: Equivalent to:
 
 ```cpp
-return @*iterator*@{it} -= n;
+return @*iterator*@(it) -= n;
 ```
 
 :::
@@ -1579,8 +1581,7 @@ return std::visit(
 ((is_nothrow_invocable_v<decltype(ranges::iter_move), 
                            const iterator_t<@_maybe-const_@<Const, Views>>&> &&
   is_nothrow_convertible_v<range_rvalue_reference_t<@_maybe-const_@<Const, Views>>,
-                             common_reference_t<range_rvalue_reference_t<
-                               @_maybe-const_@<Const, Views>>...>>) &&...)
+                           @*concat-rvalue-reference-t*@<@_maybe-const_@<Const, Views>...>>) && ...)
 ```
 
 :::

impl/concat/concat.hpp

@@ -468,14 +468,14 @@ class concat_view : public view_interface<concat_view<Views...>> {
     friend constexpr auto
     operator<=>(const iterator& x, const iterator& y) requires(
         (random_access_range<__maybe_const<Const, Views>> &&
-         three_way_comparable<__maybe_const<Const, Views>>)&&...) {
+         three_way_comparable<iterator_t<__maybe_const<Const, Views>>>)&&...) {
       return x.it_ <=> y.it_;
     }
 
     friend constexpr iterator operator+(const iterator& it,
                                         difference_type n) requires
         xo::concat_is_random_access<Const, Views...> {
-      return iterator{it} += n;
+      return iterator(it) += n;
     }
 
     friend constexpr iterator operator+(difference_type n,
@@ -487,7 +487,7 @@ class concat_view : public view_interface<concat_view<Views...>> {
     friend constexpr iterator operator-(const iterator& it,
                                         difference_type n) requires
         xo::concat_is_random_access<Const, Views...> {
-      return iterator{it} -= n;
+      return iterator(it) -= n;
     }
 
     friend constexpr difference_type operator-(const iterator& x,
@@ -567,8 +567,7 @@ class concat_view : public view_interface<concat_view<Views...>> {
               const iterator_t<__maybe_const<Const, Views>>&> &&
           std::is_nothrow_convertible_v<
               range_rvalue_reference_t<__maybe_const<Const, Views>>,
-              common_reference_t<range_rvalue_reference_t<
-                  __maybe_const<Const, Views>>...>>)&&...)) {
+              xo::concat_rvalue_reference_t<__maybe_const<Const, Views>...>>)&&...)) {
       return std::visit(
           [](auto const& i) -> xo::concat_rvalue_reference_t<
                                 __maybe_const<Const, Views>...> {  //
@@ -628,7 +627,9 @@ class concat_view : public view_interface<concat_view<Views...>> {
     }
   }
 
-  constexpr auto end() const requires(range<const Views>&&...) {
+  constexpr auto end() const requires((range<const Views>&&...) &&
+                                      xo::concatable<const Views...>)
+  {
     using LastView = xo::back<const Views...>;
     if constexpr (common_range<LastView>) {
       constexpr auto N = sizeof...(Views);

impl/concat/test/basics.cpp

@@ -757,3 +757,14 @@ TEST_POINT("size") {
     auto cv2 = std::ranges::concat_view(std::views::all(v1), std::views::all(v1));
     CHECK(cv2.size() == 4);
 }
+
+TEST_POINT("spaceship")
+{
+    int a1[] = {1,2};
+    int a2[] = {3,4};
+    auto v1 = std::views::concat(a1,a2);
+
+    auto it = v1.begin();
+
+    [[maybe_unused]] auto b = it <=> it;
+}