Perhaps you should try some spelling variations:
hermann ebooks » german books
gael robert » gal robert, hall robert, ball robert
robert b » robert _, robert e, robert j
a robust » _ robust
heitmann » heimann, heinemann, hartmann
ebooks » ebookss, eebooks
book » books, ebook

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( gael robert b. hermann ebooks ) or ( a robust _. heitmann book ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( gael robert b. hermann ebooks ) OR ( a robust _. heitmann book )).
• Adding a wildcard symbol may retrieve word variants: (( gael robert b. hermann ebooks ) or ( a robust _. heitmann book ))*.