I don't use Anarki myself, but figuring this out is easy with git.
Your first step is to find out if this was working earlier in the current branch; that is, did this get broken by a later commit or was it simply never ported to Arc 3.1?
If your find an earlier commit on the branch where it was working, finding out which commit exactly broke is easy: write a small shell script that returns true or false depending on whether the feature is working, and then use git-bisect (http://www.kernel.org/pub/software/scm/git/docs/git-bisect.h...)
Once you've found the commit that broke the feature, you can either look at the change yourself and/or contact the author of the commit.
What is it that you want that code to do? I'm not sure I see why that's a bug. You seem to be providing two arguments, 0 and 1, to a function that only expects one, '_ .
The OP is presuming that anarki hacked the bracketed functions to accept multiple arguments. I remember reading that somewhere as well, but since I haven't tried using the feature before I don't really know.
Thanks, it seems like my brain was scrambled last night. _0 and _1 (or _a and _b) are the appropriate pieces of code. But the real problem was that I was operating out of an arc directing that was lacking a load/ directory. Thus I was missing the make-br-fn.arc file. Fixed now. Thanks guys!