[Xy-pic] new arrow types

Ross Moore ross@ics.mq.edu.au
Wed, 13 Mar 2002 18:55:03 +1100 (EST)

>     Hello everybody, 
> I'd like to have an xy-pic arrow looking like \subset.
>    (
>     My expirience:
>     I've tried
>               \ar@{*{\subset}}

If you want an extended "contains in" arrow, as frequently used
for an injective map in abstract algebra, algebraic geometry or
category theory (and elsewhere), then:

Try this: it should work:   \ar@{(->} 

  It uses   \dir{(}  as the tail ,  \dir{-} to build the stem
 and  \dir{>}  for the arrowhead.

If you don't want arrow-tips, then   \ar@{(-}  should do it.

However, if you want a stem constructed from \subset pieces,
then one way to do it is:

         ^^  ^^^^    ^^
          1    2      3

In general, to make customised arrows, you need to specify
 3 directional pieces.

If you give only 1 or 2 pieces, then Xy-pic tries to guess
which parts you are changing; shaft, tip or tail.

 e.g.  \ar@{>}  is the same as  \ar{->} and  \ar{{}->}
 (i.e. only the head is affected, similarly with  \ar@{(} )
but  \ar{.}   alters only the stem.

This is because it's much more common to want a dotted stem
than to have a dot as the arrow-head.

If you use a "non-standard" directional; that is,
something for which  \dir{<piece>}  is not defined,
then you need to specify it as  *{<piece>} 
(This explains the  *{\subset}  above.)

>     i.e.
>       \xymatrix
>       {
>           A \ar@{*{\subset}}[r] & B \\
>       }
>     it does not look right; and I think that XY-Pic is
>         right, becasue, according to 
>     the Users's guide, I've described the head and not
> the shaft.
>        I've also tried
>           \ar@{{}*{\subset}{}}
>      meaning an empty tail, shaft like \subset and an
> empty head;
>      it also did not work, this time I do not know
> why. 

In what way did this not work ?
You should get multiple copies of \subset, stretching between
the objects at either end -- that's certainly what I get.

The pieces will *not* be rotated to match the direction of
the arrow, but will always be horizontal.

However,  \ar@{{}{(}{}}  will use circular arcs, rotated appropriately,
since  \dir{(}  is defined as an Xy-pic directional object.

>    )
>   What is the right answer? Thank you, Maxim Leenson.

Hope this helps,

	Ross Moore

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