Perhaps you should try some spelling variations:
"a robust e. german book" » "a robust e. german books", "a robust e. german food", "_ robust e. german book", "a robust _. german book", "a robust a. german book", "a robust l1. german book"
"a robust end. german book" » "a robust end. german books", "a robust end. german food", "a robust read. german book", "a robust bound. german book", "_ robust end. german book", "a robust _nd. german book", "a robust and. german book", "a robust l1nd. german book"
"a robert _. heilman ebook" » "3 robert _. heilman ebook", "dr robert _. heilman ebook", "a robot _. heilman ebook"

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (((("a robust e. german book") or ("a robust end. german book"))) or ("a robert _. heilman ebook"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("a robust e. german book") OR ("a robust end. german book"))) OR ("a robert _. heilman ebook")).
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• Adding a wildcard symbol may retrieve word variants: (((("a robust e. german book") or ("a robust end. german book"))) or ("a robert _. heilman ebook"))*.