Perhaps you should try some spelling variations:
gael robert » gal robert, hall robert, ball robert
robert e » robert _, robert j
a robust » _ robust
book » books, ebook
eebooks » eebookss, eeebooks, ebooks, redbooks, texbooks
heilmann » hellmann, helmann, keilmann
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: (( gael robert e. (heilmann OR heitmann) book ) or ( a robust _. heilman eebooks ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( gael robert e. (heilmann OR heitmann) book ) OR ( a robust _. heilman eebooks )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( gael robert e. (heilmann OR heitmann) book ) or ( a robust _. heilman eebooks ))".
• Adding a wildcard symbol may retrieve word variants: (( gael robert e. (heilmann OR heitmann) book ) or ( a robust _. heilman eebooks ))*.