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

event A.
event B.
event C.

letfun f1(x:bitstring)=
  let (=(event A; a),=(event C;b)) = (x,event B; x) in
  a.

query attacker(sk).

process
  in(c,x:bitstring);
  out(c,f1(x))

(* EXPECTPV
RESULT not attacker(sk[]) is true.
0.000s (user 0.000s + system 0.000s), max rss 7220K
END *)
