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