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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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