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", "dung and moon letters", "cung and moon letters", "ung and moon letters"
"song and moon letters" » "song and mon letters", "song and muon letters", "song and yoon letters", "cong and moon letters", "dong and moon 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 ("song 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 ("song 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 (\"song and moon letters\"))))".
• Removing quotes may allow a broader search: (( sun and moon letters ) or ((( sung and moon letters ) OR ( song and moon letters )))).
• Adding a wildcard symbol may retrieve word variants: (("sun and moon letters") or ((("sung and moon letters") OR ("song and moon letters"))))*.