Perhaps you should try some spelling variations:
robert j » robert _, robert e
a robust » _ robust
robust e » robust _, robert e
gal » goal, gael, gail
heitmann » heimann, hermann, hartmann
book » ebook
books » ebooks
ebooks » eebooks, ebook
heilmann » heimann, hermann, hellman

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. heitmann (book or books) ) or ( a robust e. (heilmann or heinemann) ebooks ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( gal robert j. heitmann (book OR books) ) OR ( a robust e. (heilmann OR heinemann) ebooks )).
• Adding a wildcard symbol may retrieve word variants: (( gal robert j. heitmann (book or books) ) or ( a robust e. (heilmann or heinemann) ebooks ))*.