Perhaps you should try some spelling variations:
a robert » gal robert
robert e » robert _, robert j
a robust » _ robust
heilman » hellman
heilmann » hellmann, heinemann, hermann, hellman
book » books, ebook
heimann » hermann, heinemann
heitmann » heinemann, hermann, hartmann

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

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