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

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

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