set allowDiffPatterns = true.

channel c.

free a,b: bitstring [private].

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

(* EXPECTPV
RESULT Diff-equivalence cannot be proved.
0.012s (user 0.012s + system 0.000s), max rss 8636K
END *)
