Perhaps you should try some spelling variations:
gal robert » hall robert
robert j » robert _
a robert » 3 robert, dr robert, a robust
robert e » robert _
book » ebook
books » ebooks
ebooks » eebooks, ebook, redbooks, texbooks
heilmann » heilemann, heimann, heilman

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