Boolean operators
Boolean operators combine terms in logical combinations. You can use the operators AND, OR, and NOT, or their equivalent special characters, in the bts_contains() search predicate.
By default, the OR operator is assumed if you do not supply a Boolean operator between two terms. However, you change the default operator to AND by setting the query_default_operator to AND when you create a bts index. For more information, see bts access method syntax.
The Boolean operators are not case-sensitive.