Proposed resolution:

This wording is relative to N4842.

1. Modify [stopsource], class stop_source synopsis, as indicated:

   namespace std {
     […]
   
     class stop_source {
     public:
       […]
   
       [[nodiscard]] friend bool
       operator==(const stop_source& lhs, const stop_source& rhs) noexcept;
       [[nodiscard]] friend bool
       operator!=(const stop_source& lhs, const stop_source& rhs) noexcept;
       friend void swap(stop_source& lhs, stop_source& rhs) noexcept;
     };
   }
   

2. Modify [stopsource.cmp] and [stopsource.special] as indicated:

   32.3.4.3 Non-member functionsComparisons [stopsource.nonmemberscmp]

   [[nodiscard]] bool operator==(const stop_source& lhs, const stop_source& rhs) noexcept;
   

   -1- Returns: true if lhs and rhs have ownership of the same stop state or if both lhs and rhs do not have ownership of a stop state; otherwise false.

   [[nodiscard]] bool operator!=(const stop_source& lhs, const stop_source& rhs) noexcept;
   

   -2- Returns: !(lhs==rhs).

   32.3.4.4 Specialized algorithms [stopsource.special]

   friend void swap(stop_source& x, stop_source& y) noexcept;
   

   -1- Effects: Equivalent to: x.swap(y).

[ 2020-01-14 Status set to Tentatively Ready after six positive votes on the reflector. ]

Just like stop_token (see LWG 3254), stop_source in [stopsource] declares an operator!= friend that is unnecessary in light of the new core language rules and should be struck.