> For the complete documentation index, see [llms.txt](https://help.cabi.org/cabi-digital-library-help/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.cabi.org/cabi-digital-library-help/search/boolean-operators.md).

# Boolean Operators

Boolean operators AND, OR, NOT can be applied to searches. Boolean operators must be capitalised, otherwise they are parsed as search terms not as Boolean operators. The symbols &&, ||, !! can also be used instead of the words AND, OR, NOT (please note the symbols must be preceded and followed by a space)

<table data-full-width="false"><thead><tr><th>Boolean Operator</th><th>Application</th></tr></thead><tbody><tr><td>AND (also &#x26;&#x26; )</td><td><p>Search for documents containing two or more terms. Each returned search result must contain all of the searched for terms.</p><p> </p><p>For example the following queries return search results containing both cat and dog.</p><p>·         cat AND dog</p><p>·         cat &#x26;&#x26; dog</p></td></tr><tr><td>OR (also || )</td><td><p>Search for documents containing at least one of two or more searched terms.</p><p> </p><p>For example the following queries return documents containing only the term cat, documents containing only the term dog, and documents containing both cat and dog.</p><p>·         cat OR dog</p><p>·         cat || dog</p></td></tr><tr><td>NOT (also !! )</td><td><p>Search for documents that do not contain a given term.</p><p> </p><p>For example the following queries return documents containing cat but not containing dog;</p><p>·         cat NOT dog</p><p>·         cat !! dog</p></td></tr></tbody></table>

{% hint style="info" %}
**Note**: For guidance on using parentheses `( )` with Boolean operators to structure complex searches, see <https://help.cabi.org/cabi-digital-library-help/search/using-boolean-operators-and-parentheses-in-advanced-search>
{% endhint %}


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