fun add2(bitstring, bitstring, bitstring, bitstring) : bitstring
     reduc forall a:bitstring, b:bitstring; add2(a,a) = a.

free tmp : channel.
const null : bitstring.
process
      (in(tmp,x:bitstring) | out(tmp, null))

(* EXPECTPV
Error: Function add2 expects 4 argument(s) but is here given 2 argument(s).
xtime: error in child process (status : 2)
END *)
