cl-union is an autoloaded compiled Lisp function in `cl-seq.el'.

(cl-union LIST1 LIST2 [KEYWORD VALUE]...)

Combine LIST1 and LIST2 using a set-union operation.
The resulting list contains all items that appear in either LIST1 or LIST2.
This is a non-destructive function; it makes a copy of the data if necessary
to avoid corrupting the original LIST1 and LIST2.

Keywords supported: :test :test-not :key