Perhaps you should try some spelling variations:
robert e » robert _
robert j » robert _
a robust » _ robust
heilmann » heilemann, heimann, heitmann, hellmann, helmann, keilmann
book » books
ebook » ebooks
ebooks » ebookss, books, redbooks, texbooks
heilman » hellman, helman, keilman

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( hall ((robert e) OR (robert j)). heilmann (book or ebook) ) or ( a robust _. heilman ebooks ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( hall ((robert e) OR (robert j)). heilmann (book OR ebook) ) OR ( a robust _. heilman ebooks )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( hall ((robert e) OR (robert j)). heilmann (book or ebook) ) or ( a robust _. heilman ebooks ))".
• Adding a wildcard symbol may retrieve word variants: (( hall ((robert e) OR (robert j)). heilmann (book or ebook) ) or ( a robust _. heilman ebooks ))*.