Thanks Alex.
So, a better description of diff might be "Returns all the elements in the
first argument that are not in the second argument"?

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On Sun, Nov 27, 2016 at 2:45 AM, Alexander Burger <a...@software-lab.de>
wrote:
> On Sat, Nov 26, 2016 at 09:05:44PM -0500, Bruno Franco wrote:
> > I was trying out the diff function and I noticed something:
> >
> > : (diff '(1 2 3 4) '(3 4))
> > -> (1 2)
> >
> > but
> >
> > : (diff '(3 4) '(1 2 3 4))
> > -> NIL
> >
> > I think this means that there is an order to the arguments of diff, where
>
> It is analogous to the arithmetic difference, where A - B is not the
> same as B - A.
>
>
> > the second argument must be the shortest.
>
> This is not the case. The length is not relevant:
>
> : (diff (1 2 3) (8 6 4 2))
> -> (1 3)
>
>
> > I also tried this:
> >
> > : (diff (1 2 3 4) 2)
> > -> (1 3 4)
> >
> > So, why does diff work even if the second argument isn't a list?
>
> This is a result of how 'diff' is implemented internally. It takes all
> elements into account, I think it is a welcome feature. Note that this
> also works:
>
> : (diff (1 2 3) (1 . 2))
> -> (3)
>
> ♪♫ Alex
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