Document(
  Prefix(ex   <http://example.org/example#>)
  Prefix(func <http://www.w3.org/2007/rif-builtin-function#>)
  
  Group  (
    Forall ?x ( ex:a(External(func:numeric-add(?x 1))) :- ex:a(?x) )
    ex:a(1)
  ) 
)