subsequent rows values difference

gistfile1.sql

sqlite> select * from t1;
i	n
a	1
b	2
c	3
d	4
e	5
foo	15
bar	37
baz	115
zzz	85
sqlite> select t1.i, t2.i, t1.n, t2.n, t1.n-t2.n as difference from t1, t1 as t2 where t1.oid=t2.oid+1;
i	i	n	n	difference
b	a	2	1	1
c	b	3	2	1
d	c	4	3	1
e	d	5	4	1
foo	e	15	5	10
bar	foo	37	15	22
baz	bar	115	37	78
zzz	baz	85	115	-30