Perhaps you should try some spelling variations:
a robust » _ robust
a robot » _ robot
robot 5 » robot _, robot 1, robot k
heilmann » heilemann, heimann, heilman
book » books, ebook
eebooks » eebookss, eeebooks
texbooks » texbookss, texebooks
heitmann » heimann, heinemann, hartmann

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( a robot 5. heilmann book ) or ( a robust _. heitmann (eebooks OR texbooks) ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( a robot 5. heilmann book ) OR ( a robust _. heitmann (eebooks OR texbooks) )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( a robot 5. heilmann book ) or ( a robust _. heitmann (eebooks OR texbooks) ))".
• Adding a wildcard symbol may retrieve word variants: (( a robot 5. heilmann book ) or ( a robust _. heitmann (eebooks OR texbooks) ))*.