Proposed resolution:

This wording is relative to N5054.

The proposed resolution completely removes the precondition on private constructor iterator(const T* value, index-type b = index-type()), as it is private and can only be invoked by the library internally.

1. Modify [range.repeat.iterator] as indicated:

   constexpr explicit iterator(const T* value, index-type b = index-type());
   

   -1- Preconditions: If `Bound` is not `unreachable_sentinel_t`, `b` ≥ 0.

   -2- Effects: […]

   […]

   constexpr explicit iterator& operator--();
   

   -6- Preconditions: If `Bound` is not `unreachable_sentinel_t`, current_ ≥ 0.

   -7- Effects: […]

   constexpr explicit iterator& operator+=(difference_type n);
   

   -8- Preconditions: If `Bound` is not `unreachable_sentinel_t`, current_ + `n` ≥ 0.

   -9- Effects: […]

   constexpr explicit iterator& operator-=(difference_type n);
   

   -10- Preconditions: If `Bound` is not `unreachable_sentinel_t`, current_ - `n` ≥ 0.

   -11- Effects: […]

As currently specified, the preconditions requiring current_ to be non-negative ([range.repeat.iterator] p2, p6, p8, p10) are applied only if "If Bound is not unreachable_sentinel_t". In consequence, decrementing iterator before begin is UB only if `views::repeat` specifies bound:

auto rv1 = views::repeat(1, 10);
auto it1 = std::prev(rv1.begin()); // UB
auto rv2 = views::repeat(1);
auto it2 = std::prev(rv2.begin()); // OK

On the LWG reflector Michał Dominiak (the author of the paper) confirmed, that this is unintentional copy-paste error in the wording, and the precondition should always be applied.