  gcd(other: INTEGER): INTEGER is
         -- Great Common Divisor of `Current' and `other'.
      
      require
         Current >= 0;
         other >= 0;
      do
         if other = 0 then Result := Current
         else
            Result := other.gcd(Current \\ other);
         end;    
      ensure
         Result = other.gcd(Current);
      end;
