Perhaps you should try some spelling variations:
robert j » robert e
a robust » _ robust
robust e » robust _, robert e
gal » goal, gael, gail
heitmann » heimann, heinemann, hermann
book » books
ebooks » ebookss
ebook » ebooks
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 ((robert j) OR (robert _)). heitmann book ) or ( a robust e. heilmann (ebooks or ebook) ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( gal ((robert j) OR (robert _)). heitmann book ) OR ( a robust e. heilmann (ebooks OR ebook) )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( gal ((robert j) OR (robert _)). heitmann book ) or ( a robust e. heilmann (ebooks or ebook) ))".
• Adding a wildcard symbol may retrieve word variants: (( gal ((robert j) OR (robert _)). heitmann book ) or ( a robust e. heilmann (ebooks or ebook) ))*.