Proposed resolution:

This wording is relative to N4778.

1. Change [unique.ptr.single.ctor] as indicated:

   unique_ptr(pointer p, const D& d) noexcept;
   unique_ptr(pointer p, remove_reference_t<D>&& d) noexcept;
   

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   -11- Remarks: If D is a reference type, the second constructor is defined as deleted. If D is not a reference type, tThese constructors shall not participate in overload resolution unless is_constructible_v<D, decltype(d)> is true.

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