Right now Koha uses ambiguous operators like "and" and "or." for searching. It would be much better if Koha offered the option of using unambiguous search operators.
*** Bug 8651 has been marked as a duplicate of this bug. ***
*** Bug 5515 has been marked as a duplicate of this bug. ***
This is solved by Elasticsearch using AND, OR, NOT. We probably won't solve it for Zebra now.