--- Roger Hui <[EMAIL PROTECTED]> wrote:

> Since APL days u/y is {.y when 1=#y , even when
> y is not in the domain of u .   For example:
> 
>    +/'a'
> a
> 
> It is not much of a flaw.  The only plausible
> alternative is to signal error.
> 
> The identity that is used to reason about u/y is
> 
>    u/y  <->  (u/k{.y) u (u/k}.y)
> 
> for k e. i.1+#y .
> 
   k=. 0
   u=. ,
   y=. 1
   #$(u/k{.y) u (u/k}.y)
1
   #$u/y
0
   
   k=. 1
   #$(u/k{.y) u (u/k}.y)
1
   #$u/y
0

   (u/y) -: (u/k{.y) u (u/k}.y)
0



 
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