Perhaps you should try some spelling variations:
"dung dung code snippets" » "duong dung code snippets", "ung dung code snippets", "dung ung code snippets", "dung dung cong snippets", "dung dung co snippets", "dung dung de snippets", "dung dung code slippers"
"luan van code snippets" » "luan van de snippets", "luan van hoe snippets", "luan van cong snippets", "luan van code slippers", "quan van code snippets", "lan van code snippets"
"locating bug code snippets" » "locating bug code slippers", "locating bung code snippets", "locating bugs code snippets"

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (((("dung dung code snippets") or ("luan van code snippets"))) or ("locating bug code snippets"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("dung dung code snippets") OR ("luan van code snippets"))) OR ("locating bug code snippets")).
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• Adding a wildcard symbol may retrieve word variants: (((("dung dung code snippets") or ("luan van code snippets"))) or ("locating bug code snippets"))*.