define
a.SET.1:1
a.SET.2:2
b.SET.1:1
b.SET.2:2
c.SET.1:1
c.SET.2:2
----

iter
seek-ge a
seek-ge b
seek-ge c
seek-ge d
seek-lt a
seek-lt b
seek-lt c
seek-lt d
seek-prefix-ge a
seek-prefix-ge b
seek-prefix-ge c
seek-prefix-ge d
----
a:2
b:2
c:2
.
.
a:1
b:1
c:1
a:2
b:2
c:2
.

iter
first
next
next
prev
prev
prev
next
next
next
next
next
next
prev
prev
next
prev
prev
next
next
next
next
prev
----
a:2
a:1
b:2
a:1
a:2
.
a:2
a:1
b:2
b:1
c:2
c:1
c:2
b:1
c:2
b:1
b:2
b:1
c:2
c:1
.
c:1
