Perhaps you should try some spelling variations:
hieu xanh » chieu xanh, hieu manh, hieu nganh
trinh dap » trinh lap, trinh da, trinh dan
dung cong » dung trong
doc hieu » toc thieu, hoc thieu, hoc hien
trinh ap » trinh lap, trinh phap, trinh nhap
cong van » cong vang, cong san, song van
van than » van thanh, van thang, van tuan
than cau » toan cau, phan cau, than cap

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

• If you are trying to use Boolean operators, they must be ALL CAPS: doc hieu xanh - hanh ((trinh ap) OR (trinh dap)) dung cong van than cau~.
• Adding a wildcard symbol may retrieve word variants: doc hieu xanh - hanh ((trinh ap) or (trinh dap)) dung cong van than cau*.