#include <ostream> // see [ostream.syn]
namespace std {
template<class charT, class traits, class Allocator>
class basic_syncbuf;
using syncbuf = basic_syncbuf<char>;
using wsyncbuf = basic_syncbuf<wchar_t>;
template<class charT, class traits, class Allocator>
class basic_osyncstream;
using osyncstream = basic_osyncstream<char>;
using wosyncstream = basic_osyncstream<wchar_t>;
}