free c:channel.

fun h(bitstring):bitstring.

const a,b:bitstring.

free k:bitstring [private].

event A(bitstring).
event B.

const ok,ko:bitstring.

not attacker(k).

process
  in(c,x:bitstring);
  out(c,k);
  if x = diff[a,b]
  then
    event A(a);
    out(c,diff[k,k])
  else
    out(c,ko)

(* EXPECTPV
RESULT Observational equivalence cannot be proved.
0.024s (user 0.016s + system 0.008s), max rss 8808K
END *)
