2 | 25. z: B List 26. u1: B 27. v: B List 28. a:{s:A| M(s) M(H(j,u)) }.
v N(j,u)

Q(j
,a
,list_accum(s',i'.process s' i' where
process s i ==
if P(i,s) then F(i,s)
else G(i,s) where
xs := N(i,s);
s:= H(i,s);
while not null xs {
s := process s (hd xs);
xs := tl xs;
} ;a;v)) 29. a: {s:A| M(s) M(H(j,u)) } 30. [u1 / v] N(j,u) Q(j,a,list_accum(s',i'.process s' i' where process s i == if P(i,s) then F(i,s) else G(i,s) where xs := N(i,s); s:= H(i,s); while not null xs { s := process s (hd xs); xs := tl xs; } ;process a u1 where process s i == if P(i,s) then F(i,s) else G(i,s) where xs := N(i,s); s:= H(i,s); while not null xs { s := process s (hd xs); xs := tl xs; } ;v)) | 7 steps |