Perhaps you should try some spelling variations:
thanh vai » thanh hai, thanh van, thanh tai
van thanh » ban thanh, van tuan
thu sach » tu sach, thuat sach, thuoc sach
luc van » luoc van, luu van, duc van
la tren » loai tren, dua tren, dat tren
mai hoi » mai khoi, dai hoi, lai hoi
ty hang » ly hang, ty xang, thi hang
ty lang » tay lang, ty xang, tu lang
ve cac » va cac, vien cac
vai la » tai la, vai va
ve cau » ke cau, va cau, le cau

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

• Performing a fuzzy search may retrieve terms with similar spellings: thu sach ((ty lang) OR (ty hang)) mai hoi. hieu ((ve cau) or (ve cac)) luc van thanh vai la tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach ((ty lang) OR (ty hang)) mai hoi. hieu ((ve cau) OR (ve cac)) luc van thanh vai la tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach ((ty lang) OR (ty hang)) mai hoi. hieu ((ve cau) or (ve cac)) luc van thanh vai la tren".
• Adding a wildcard symbol may retrieve word variants: thu sach ((ty lang) OR (ty hang)) mai hoi. hieu ((ve cau) or (ve cac)) luc van thanh vai la tren*.