Perhaps you should try some spelling variations:
cau thuc » cau truc, cuu thuc, can thuc
vat hanh » vat thanh, van hanh, nhat hanh
tay thai » lay thai, toc thai, y thai
so sach » so sanh, bo sach, co sach
tai cua » thai cua, tai cuc, tri cua
va hanh » van hanh, va thanh, va danh
hieu ve » hieu va, hieu van
tay hoi » tay ho, tao hoi
sach ly » sach y, sach lo, sach ty
ly hang » ly quang
cua tre » cua te, cuu tre, cua triet
ve cau » ke cau, va cau, ve cac

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ly hang ((tay hoi) or (tay thai)). hieu ve cau thuc ((vat hanh) OR (va hanh)) tai cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ly hang ((tay hoi) OR (tay thai)). hieu ve cau thuc ((vat hanh) OR (va hanh)) tai cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ly hang ((tay hoi) or (tay thai)). hieu ve cau thuc ((vat hanh) OR (va hanh)) tai cua tre".
• Adding a wildcard symbol may retrieve word variants: so sach ly hang ((tay hoi) or (tay thai)). hieu ve cau thuc ((vat hanh) OR (va hanh)) tai cua tre*.