# code: http://golf.shinh.org/reveal.rb?stable+partition/darrenks_1640230125&nbb
# target Nibbles version: 0.25
# commenter version: 0.1.3.183

+ #(concat):[chr] 
    =~ #(group by (also sorts)):[[chr]] 
        fstLine #(@):[chr] 
        \A 
        `$ #(signum):int 
            - #(subtract):int 
                A #($):chr 
                / #(foldr1):chr 
                    fstLine #(_):[chr] 
                    #\C B 
                    #(implicit arg = C):chr