Perhaps you should try some spelling variations:
nhung cong » dung cong, thong cong, hang cong
hieu lang » chieu sang, hieu quang, nhieu tang
trinh han » trinh quan
hai hieu » hai chieu, hoi hieu, phan hieu
tan toan » tan tran, van toan, dan toan
tap toan » tap doan, tap quan, bai toan
luat » luan, xuat

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: hai hieu lang - hanh ((trinh luat) OR (trinh han)) nhung cong ((tan toan) OR (tap toan)) cau~.
• Adding a wildcard symbol may retrieve word variants: hai hieu lang - hanh ((trinh luat) or (trinh han)) nhung cong ((tan toan) or (tap toan)) cau*.