Perhaps you should try some spelling variations:
ve triet » va trien
su triet » su viet, su tien
tinh vi » trinh vi, tinh voi, tinh va
va tinh » may tinh
cac toc » cac toi, cac nuoc, cac thoi
sach ty » sach y, sach tu, sach thu
tu sach » thu sach, su sach, te sach
ty lang » tay lang, ty xang, ty hang
hieu ve » hieu va, hieu van
toc va » hoc va, toc ta, tuc va
ve cac » va cac, vien cac
o hai » co hai, so hai, o lai
o hoi » co hoi, o hoc, o hoa

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: tu sach ty lang ((o hoi) or (o hai)). hieu ve cac toc va tinh vi ((su triet) OR (ve triet))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach ty lang ((o hoi) OR (o hai)). hieu ve cac toc va tinh vi ((su triet) OR (ve triet)).
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach ty lang ((o hoi) or (o hai)). hieu ve cac toc va tinh vi ((su triet) OR (ve triet))".
• Adding a wildcard symbol may retrieve word variants: tu sach ty lang ((o hoi) or (o hai)). hieu ve cac toc va tinh vi ((su triet) OR (ve triet))*.