Hi,
I'm trying to evaluate this problem using Z3's DataLog engine:

(set-option :fixedpoint.engine datalog)
(define-sort s () String)

(declare-rel edge (s s))
(declare-rel path (s s))

(declare-var a s)
(declare-var b s)
(declare-var c s)

(rule (=> (edge a b) (path a b)) P-1)
(rule (=> (and (path a b) (path b c)) (path a c)) P-2)

(rule (edge "s1" "s2") E-1)
(rule (edge "s2" "s3") E-2)
(rule (edge "s3" "s1") E-3)

(declare-rel cycle (s))
(rule (=> (path a a) (cycle a)))
(query cycle :print-answer true)

My version of Z3 (Z3.4.8.0) aborts with the error: " (error "query failed: Rule contains infinite sorts in rule P-1: path(#1,#0) :- edge(#1,#0). ") unknown" if strings are used.
It works with BitVec and Ints but in my problem I need to use Strings.
If i understand, the String variables type is not supported.