set allowDiffPatterns = true.

channel c.

free a,b: bitstring [private].

process
      in(c, in_t: bitstring);
      let diff[y,z] = in_t in
      out(c, (y,z))
      |
      out(c, diff[a,b])

(* EXPECTPV
RESULT Diff-equivalence cannot be proved.
0.016s (user 0.016s + system 0.000s), max rss 8620K
END *)
