LWG3849 cartesian_product_view::iterator's default constructor is overconstrained

Author: burblebee

source/ranges.tex

@@ -14475,7 +14475,7 @@
       range_reference_t<@\exposid{maybe-const}@<Const, Vs>>...>;
     using difference_type = @\seebelow@;
 
-    @\exposid{iterator}@() requires @\libconcept{forward_range}@<@\exposid{maybe-const}@<Const, First>> = default;
+    @\exposid{iterator}@() = default;
 
     constexpr @\exposid{iterator}@(@\exposid{iterator}@<!Const> i) requires Const &&
       (@\libconcept{convertible_to}@<iterator_t<First>, iterator_t<const First>> &&