Perhaps you should try some spelling variations:
"dong tac bo sung tai lieu." » "dong tai bo sung tai lieu." (Expand Search), "dong bac bo sung tai lieu." (Expand Search), "dong tay bo sung tai lieu." (Expand Search), "dong tac bo dung tai lieu." (Expand Search), "dong tac bo dong tai lieu." (Expand Search), "dong tac bo vung tay lieu." (Expand Search), "dong tac bao sung tai lieu." (Expand Search), "dong lac bo sung tai lieu." (Expand Search)
"cong tac bo dung tin lieu." » "cong tac bo dung tin hieu." (Expand Search), "cong tac bo dung tin lien." (Expand Search), "cong tac bo dung tin tieu." (Expand Search), "cong tac bo duong tin lieu." (Expand Search), "cong tac bao dung tin lieu." (Expand Search), "cong tac bo tung tin lieu." (Expand Search), "cong bac bo dung tin lieu." (Expand Search), "cong lac bo dung tin lieu." (Expand Search)

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• Performing a fuzzy search may retrieve terms with similar spellings: (("dong tac bo sung tai lieu.") OR ("cong tac bo dung tin lieu."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"dong tac bo sung tai lieu.\") OR (\"cong tac bo dung tin lieu.\"))".
• Removing quotes may allow a broader search: (( dong tac bo sung tai lieu. ) OR ( cong tac bo dung tin lieu. )).
• Adding a wildcard symbol may retrieve word variants: (("dong tac bo sung tai lieu.") OR ("cong tac bo dung tin lieu."))*.