Proposed resolution:

1. Remove [alg.replace]/1.

   template<ForwardIterator Iter, class T> 
     requires OutputIterator<Iter, Iter::reference> 
           && OutputIterator<Iter, const T&> 
           && HasEqualTo<Iter::value_type, T> 
     void replace(Iter first, Iter last, 
                  const T& old_value, const T& new_value); 
   
   template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred, class T> 
     requires OutputIterator<Iter, Iter::reference> 
           && OutputIterator<Iter, const T&> 
           && CopyConstructible<Pred> 
     void replace_if(Iter first, Iter last, 
                     Pred pred, const T& new_value);
   

   1 Requires: The expression *first = new_value shall be valid.

2. [alg.replace]/4: Remove the sentence "The results of the expressions *first and new_value shall be writable to the result output iterator.".

   template<InputIterator InIter, typename OutIter, class T> 
     requires OutputIterator<OutIter, InIter::reference> 
           && OutputIterator<OutIter, const T&> 
           && HasEqualTo<InIter::value_type, T> 
     OutIter replace_copy(InIter first, InIter last, 
                          OutIter result, 
                          const T& old_value, const T& new_value);
   
   template<InputIterator InIter, typename OutIter,
            Predicate<auto, InIter::value_type> Pred, class T> 
     requires OutputIterator<OutIter, InIter::reference> 
           && OutputIterator<OutIter, const T&> 
           && CopyConstructible<Pred> 
     OutIter replace_copy_if(InIter first, InIter last, 
                             OutIter result, 
                             Pred pred, const T& new_value);
   

   4 Requires: The results of the expressions *first and new_value shall be writable to the result output iterator. The ranges [first,last) and [result,result + (last - first)) shall not overlap.

[ Batavia (2009-05): ]

We agree with the proposed resolution.

Move to Tentatively Ready.

(A) [alg.replace]/1:

Requires: The expression *first = new_value shall be valid.

(B) [alg.replace]/4:

Requires: The results of the expressions *first and new_value shall be writable to the result output iterator.[..]

Since conceptualization, the quoted content of these clauses is covered by the existing requirements

(A) OutputIterator<Iter, const T&>

and

(B) OutputIterator<OutIter, InIter::reference> && OutputIterator<OutIter, const T&>

resp, and thus should be removed.