title: how to get constraint of variable in Fixedpoint using z3?
body: <p>I wish to get the constraint of the element in the fixedpoint phi like d>=0.0, how to realize it in Z3?</p>
  
  <pre><code>(set-option :produce-models true)
  (set-option :dl_engine 1)
  (set-option :dl_pdr_use_farkas true)
  (declare-var c Real)
  (declare-var d Real)
  (declare-var lambda Real)
  (declare-rel phi(Real))
  (rule 
     (=&gt;
        (and
          (&gt;= lambda 0.0)
          (phi c)
        )
        (phi (+ c lambda))
     )
  )
  (rule 
      (=&gt;
         (= c 0.0)
         (phi c)
      )
  )
  (rule
       (=&gt;
          (phi c)
          (phi d)
       )
   )
  (query (phi d))
  </code></pre>