Perhaps you should try some spelling variations:
"sun and moon letters" » "sun and mon letters", "sun and muon letters", "sun and yoon letters"
"sung and moon letters" » "sung and mon letters", "sung and muon letters", "sung and yoon letters", "song and moon letters", "cung and moon letters", "ung and moon letters"
"dung and moon letters" » "dung and mon letters", "dung and muon letters", "dung and yoon letters"

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("sun and moon letters") or ((("sung and moon letters") OR ("dung and moon letters"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("sun and moon letters") OR ((("sung and moon letters") OR ("dung and moon letters")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"sun and moon letters\") or (((\"sung and moon letters\") OR (\"dung and moon letters\"))))".
• Removing quotes may allow a broader search: (( sun and moon letters ) or ((( sung and moon letters ) OR ( dung and moon letters )))).
• Adding a wildcard symbol may retrieve word variants: (("sun and moon letters") or ((("sung and moon letters") OR ("dung and moon letters"))))*.