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

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

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