:;; insertion
= _ 5+ ! 6+ ! 7+ ! 8+ ! 9+ ! 10+ ! 11+ D!
    1+ ! 2+ ! 3+ ! 4+ D!

:;; initial population for upcoming tests
= _ 1+ ! 2+ ! 3+ ! 4+ ! 5+ ! 6+ ! 7+ ! 8+ ! 9+ D!

:
:;; lookup
5 ?n 10 ?n

:
:;; path motion
"
[pk >pk >pk >pk -
]pk <pk <pk
5@ p < pk
4@ p < p
4@ p > p
0@ p > p
10@ p < p
)

:
:;; remove
" 7k- ! 6k- ! 4k- ! [k- ! ]<<k- ! 2k- ! 3k- ! 8k- ! 9k- i ! )

:
:;; join
" i ( 11+ 13+ 12+ i! *k ~ D! )
" i ( 11+ 13+ 12+ i! 10k ~ D! )
" i ( 11+ i! 10k ~ D! )
" i ( i! 10k ~ D! )
" i ( i! *k ~ D! )
" i ( 11+ 12+ 13+ 14+ 15+ 16+ 17+ 18+ 19+ 20+ i! 10k ~ D! )

:
:;; split
=_ # 31 i! 18@ p / D! ) D! ) D!
=_ # 31 17- i! 17@ p / D! ) D! ) D!
=_ # 31 19- i! 19@ p / D! ) D! ) D!

:
:;; set ops
= _
   1+  3+  5+  7+  9+ 11+ 13+ 15+ i!
(  2+  3+  6+  7+ 10+ 11+ 14+ 15+ i!
|
:union
D! )
:intersection
D!

= _
:a
   1+  3+  5+  7+  9+ 11+ 13+ 15+ i!
:b
(  2+  3+  6+  7+ 10+ 11+ 14+ 15+ i!
\
:difference
D! )
:intersection
D! )
:a original
D!

:
:;; clear everything.
= _