# This is an example of a type annotation and an or-type.
# The function inverts its input.
( ((\in ->
     (|retone|rettwo| <+
        in$[|[->$retone]
	    # Note both the pattern and value of type True
	    # are syntactically empty (before and after the ->).
            |[->$rettwo]|]
     ) 
   ) : (| True | True |) -> (| True | True |)
  )
  be (\@x->x)
)