fun h(bitstring):channel.
free a:bitstring.
free b:bitstring.
free c:channel.
free k:bitstring [private].
event A.

process
  in(diff[h(a),h(a)],x:bitstring); out(c,diff[a,b]); event A

(* EXPECTPV
RESULT Observational equivalence cannot be proved.
0.016s (user 0.016s + system 0.000s), max rss 8604K
END *)
