% transpose is defined in initlib like this.
/transpose {
    [ exch {
        { {empty? exch pop} map all?} {pop exit} ift
        [ exch {} {uncons {exch cons} dip exch} fold counttomark 1 roll]
 uncons
    } loop ] {reverse} map
}.

% using it.
[[/a /b /c] [/A /B /C] [1 2 3]] transpose