Perhaps you should try some spelling variations:
"a robust e. hellman book" » "a robust e. german book", "_ robust e. hellman book", "a robust _. hellman book", "a robust a. hellman book", "a robust end. hellman book"
"a robert j. heitmann book" » "3 robert j. heitmann book", "dr robert j. heitmann book", "a robot j. heitmann book", "a robert _. heitmann book", "a robert e. heitmann book"
"a robust e. hellman joel" » "_ robust e. hellman joel", "a robust _. hellman joel", "a robust a. hellman joel", "a robust end. hellman joel"

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• Performing a fuzzy search may retrieve terms with similar spellings: (("a robert j. heitmann book") or ((("a robust e. hellman book") OR ("a robust e. hellman joel"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("a robert j. heitmann book") OR ((("a robust e. hellman book") OR ("a robust e. hellman joel")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"a robert j. heitmann book\") or (((\"a robust e. hellman book\") OR (\"a robust e. hellman joel\"))))".
• Removing quotes may allow a broader search: (( a robert j. heitmann book ) or ((( a robust e. hellman book ) OR ( a robust e. hellman joel )))).
• Adding a wildcard symbol may retrieve word variants: (("a robert j. heitmann book") or ((("a robust e. hellman book") OR ("a robust e. hellman joel"))))*.