What is OR and AND?

You can add several search strings for two different reasons, either you want to get an item if any string is hitting it, the OR logic, or you want to get an item only if all the strings are hitting it, the AND logic. The latter technique can be preferred if you are looking for a specific publication you know about, or if you have specific knowledge about the data base, which you normally don't, - the former is preferred if you without specific knowledge are searching for instance on a subject or author, which you normally are.
The search engine is case-sensitive. But in the OR search, if a leading letter is lower-case, the search also includes the leading letter as upper-case, and if any other letter is lower-case, the search also includes all letters as upper-case. Therefore, the OR logic search is normally preferred, with the use of lower-case rather than upper-case letters when guessing.

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