free c:channel.

fun h(bitstring):bitstring.

const a,b:bitstring.

event A(bitstring).

const ok,ko:bitstring.

lemma x:bitstring,y:bitstring; event(A(x)) ==> x=a [maxSubset].

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

(* EXPECTPV
RESULT event(A(x_1)) ==> x_1 = a cannot be proved.
RESULT Observational equivalence cannot be proved.
0.044s (user 0.032s + system 0.012s), max rss 8960K
END *)
