deferred class interface NUMERIC
   --
   -- This class describes a ring.
   --

feature(s) from HASHABLE   hash_code: INTEGER
      -- The hash-code value of Current.

      ensure
         good_hash_value: Result >= 0

feature(s) from NUMERIC   infix "+" (other: like Current): like Current
      -- Sum with other (commutative).
      --      require
      --        other /= Void


   infix "-" (other: like Current): like Current
      -- Result of substracting other.
      --      require
      --         other /= Void


   infix "*" (other: like Current): like Current
      -- Product by other.
      --      require
      --         other /= Void


   infix "/" (other: like Current): NUMERIC
      -- Division by other.

      require
         other /= Void;
         divisible(other)

   prefix "+": like Current
      -- Unary plus of Current.


   prefix "-": like Current
      -- Unary minus of Current.


   divisible (other: like Current): BOOLEAN
      -- May Current be divided by other ?

      require
         other /= Void

   one: like Current
      -- Neutral element for "*" and "/".


   zero: like Current
      -- Neutral element for "+" and "-".


   sign: INTEGER_8
      -- Sign of Current (0 -1 or 1).

      ensure
         -1 <= Result;
         Result <= 1



end of deferred NUMERIC