link image

procedure main()
    while writes("Line? ") & line := read() do {
        writes(line)
        line ? {
            as := tab(many('a')) &
            bs := tab(many('b')) &
            cs := tab(many('c')) &
            *as = *bs = *cs & pos(0) & write(": Yes")
            } | write(": No")
        }
end