set FOR = for-up a,i,n,I;
set i1 = a,i >=0_goto ((card I) + 3);
set i2 = AddTo a,i,n;
set PF = ((Load (a,i >=0_goto ((card I) + 3))) ';' I) ';' (AddTo a,i,n);
card (((Load (a,i >=0_goto ((card I) + 3))) ';' I) ';' (AddTo a,i,n)) =
(card ((a,i >=0_goto ((card I) + 3)) ';' I)) + 1
by SCMP_GCD:8
.=
((card I) + 1) + 1
by SCMPDS_6:15
.=
(card I) + (1 + 1)
;
then
(card (((Load (a,i >=0_goto ((card I) + 3))) ';' I) ';' (AddTo a,i,n))) + (- ((card I) + 2)) = 0
;
hence
for-up a,i,n,I is shiftable
by SCMPDS_4:78; verum