Set functions

The Set functions are the instructions which define the group of documents for a query. These functions predicate functions, combining/merging functions, and relationship functions. Every set function returns a set reference (or SetRef for short) which can be materialized with the Paginate function, providing cursor semantics over the resulting set.

Set functions return ad hoc set predicates based on their arguments. They can be composed to create more complex sets. The paginate function is used to access a set’s elements and historical timeline.

`Difference`	Returns the set of items in one set that are missing from additional sets.
`Distinct`	Returns the set of distinct items within a set.
`Events`	Returns the set of events describing the history of a set/ref.
`Intersection`	Returns the set of items that exist in all sets.
`Join`	Combines the items in a set with set’s indexed values.
`Match`	Returns the set of items that match search terms.
`Singleton`	Returns a set containing the first item of a set.
`Union`	Returns a set that combines the items in multiple sets.