Document(
  Prefix(ex   <http://example.org/example#>)
  Prefix(func <http://www.w3.org/2007/rif-builtin-function#>)
  Prefix(pred <http://www.w3.org/2007/rif-builtin-predicate#>)
  
  Group  (
    Forall ?x ( ex:a(External(func:numeric-subtract(?x 1))) :- 
                    And ( ex:a(?x) External(pred:numeric-greater-than-or-equal(?x 0)))
    )
    ex:a(10)
  ) 
)