
event e(bitstring).

const a,b: bitstring.

lemma x: bitstring; event(e(x)) ==> false.

channel c.

equivalence
(in(c, x: bitstring); event e(a); if x = a then out(c, a)) | (in(c, x: bitstring); event e(b); if x = b then out(c, a))
(in(c, x: bitstring); event e(b); if x = b then out(c, a)) | (in(c, x: bitstring); event e(a); if x = a then out(c, a))

(* EXPECTPV
RESULT not event(e(x_4)) is true.
RESULT Observational equivalence cannot be proved.
RESULT not event(e(x_4)) is false.
0.064s (user 0.048s + system 0.016s), max rss 9256K
END *)
