•chemotherapy AND "eye cancer" OR retinoblastoma
–retrieves entries containing the keyword “retinoblastoma” without the word “chemotherapy.” Any retrieved entries with “chemotherapy” also contain “eye cancer.”
•In contrast:
•chemotherapy AND ("eye cancer" OR retinoblastoma)
–retrieves entries with the keyword “chemotherapy” that additionally contain either "eye cancer" or “retinoblastoma.”
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