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Nub Sieve ~:  _ 0 0 Not Equal

~:y is the boolean list b such that b#y is the nub of y . For example:
   ~: 'Mississippi'
1 1 1 0 0 0 0 0 1 0 0
  x~:y is 1 if x is tolerantly unequal to y . See Equal (=).

The fit conjunction may be used to specify tolerance, as in ~:!.t .
 

The result of nub-sieve can be used to select the nub as follows:
   y=: 8 1 8 2 8 1 7 2
   ~. y
8 1 2 7

   ~: y 
1 1 0 1 0 0 1 0

   (~: y) # y
8 1 2 7

   y #~ ~: y
8 1 2 7
The dyad ~: applies to any argument, but for booleans it is called exclusive-or. For example:
   d=: 0 1
   d ~:/ d
0 1
1 0
Not-equal, not equal, and the dual of equal with respect to not, all agree as illustrated below.
   (~:/ ; -.@=/ ; =&.-./)~ d
+---+---+---+
|0 1|0 1|0 1|
|1 0|1 0|1 0|
+---+---+---+


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