(* The query is false because the communication on channel c
   between out(c,a) and in(c,=a) can be private,
   so the attacker may have b without having a *)

free c:channel.
free a:bitstring [private].
free b:bitstring [private].

query x:bitstring; attacker(b) ==> attacker(a).

set verboseClauses = short.

process
  (out(c,a) | in(c,=a); out(c,b))

(* EXPECTPV
RESULT attacker(b[]) ==> attacker(a[]) cannot be proved.
0.008s (user 0.004s + system 0.004s), max rss 7296K
END *)
