[Inquiry] Re: Theme One Program -- Commentary -- Knot

[Jon Awbrey]

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TOP.  Commentary Note 42

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Knot.

Knot is a transformation of ideas that acts as a predicate recognizer.
Its functional value is nil unless its argument idea points to a form
in a cycle of forms that has a form bearing a right parenthesis which
both precedes and follows the argument idea in the cycle of forms, in
which situation the argument idea is returned as the functional value.

The following two cases are the only ones that return
a non-nil result under ordinary circumstances of use:

Case 1.

     o---------o
     |  o---o  |
     o->| ) |--o
        o---o
        ^
   this | = knot (this)
        @

Case 2.

     o----------------o
     |  o---o  o---o  |
     o->|   |->| ) |--o
        o---o  o---o
        ^
   this | = knot (this)
        @

function knot (this: idea): idea;
begin
 knot := equity (this, equity (fore (suit (this)), next (suit (this))))
end;

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