Example One

let $X_1 = X_2 = X_3 = \{0,1\}*$ (all binary strings (*)). Let P = `` $h := a; a := b; b := h$''. The state vector generally is $(h,a,b) \in X = x_1\;$x$\;x_2\;$x$\;x_3$ Supose input vector is $x = (110,01,1001)$.

before:	code:	after:
$(110,01,1001)$	$h:=a$	$(01,01,1001)$
$(01,01,1001)$	$a:=b$	$(01,1001,1001)$
$(01,1001,1001)$	$b:=h$	$(01,1001,01)$

Generally, if the input vector is $(p,q,r)$, then the output is determined via: $(p,q,r) \mapsto (q,q,r) \mapsto (q,r,r) \mapsto (q,r,q)$ so the second and third positions are swapped, and the value originally in the first position is lost.