# code: http://golf.shinh.org/reveal.rb?stable+partition/darrenks_1640230125&nbb
# target Nibbles version: 0.2
# commenter version: 0.1.2.181

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