E =: 0$<1
3!:0 E NB. E is boxed:
32
1;E
+-++
|1||
+-++
(<1),E
+-+
|1|
+-+
The Dictionary:
x;y is (<x),y if y is boxed, and (<x),<y if y is open.
My interest:
Properties of E as the empty set, where "set" is modeled as a sorted list of
boxes, without repetitions, and "element" is the array contained in a box.
IsSet =: [: *./ (-: /:~),(-: ~.),(1 = #...@$),(32 = 3!:0)
IsSet E
1
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