[591] % cvc4 -q --strings-exp small.smt2
sat
[592] % cvc4 -q --strings-exp --re-elim --re-elim-agg small.smt2
unsat
[593] % cat small.smt2
(declare-fun a () String)
(declare-fun b () String)
(assert (str.in_re (str.++ a b) (re.* (str.to_re "A"))))
(assert (str.in_re b (re.diff (re.union (str.to_re "A") (str.to_re "B")) (re.++ (str.to_re "A") (re.* (str.to_re "B")) (str.to_re "A")))))
(check-sat)
[594] %