I'm trying to make a diagram similar to this (from wikipedia)
Except that I want to the double arrow $\eta$ two be pointing from node $B$ toward the middle of arrow $X$ (it is, after all, a natural transformation from $RF$ to $X$).
I'm trying to use the \xtwocell
command of the 2cell package for xy. In subsection 3 (Excursions) of section 25.4 (extra options) of chapter 25 (two-cell) on page 47 of the xyrefer manual, it is stated
\xtwocell[⟨hop⟩]{⟨displace⟩}...
connects to the ⟨pos⟩ displaced by ⟨displace⟩ from the relative cell location specified by ⟨hop⟩. The displacement can be any string of valid XY-pic commands, but they must be enclosed within a group {...}. When the cell location is the target, a null grouping {} must be given. When used with the <\omit> nudge, such excursions allow a labelled Arrow to be placed anywhere within an XY-pic diagram; furthermore the Arrow can be oriented to point in any direction.
Of course the manual gives no examples and makes no further comment about how to change the orientation of the Arrow (in this manual, capitalized "Arrow" refers to the double arrow between arrows, i.e. the 2-cell).
What does he mean by "any string of valid XY-pic commands"? What may the displacement argument for \xtwocell
be? Any experiments I tried (eg <1>,dr,[0,1]) typing in the curly braces just ended up in the $A$ node text, so not being interpreted as a displacement or position or orientation. How do I change the orientation of the Arrow? How do I achieve the "orientation in any direction" that was promised me?
Here is my simple markup
\xymatrix{
A\ar[d]\ar[r]\xtwocell[0,1]{}\omit{<2>} & B\\
C\ar@{.>}[ur] &
}
which gives the following image
I want to change the direction that double arrow is pointing, point it to the corner object $C$, or reverse it. I can shift it by changing the number in \omit{<2>}
, but how to change the orientation?
(Google showed me that the same question is asked here on the xy mailing list, but never answered)
See also my question at Label the source/target object in the middle of compositemaps from 2cell package of xy? for another attempted method at this diagram.