( expandRanges
  =   a b L
    .     @( !arg
           :   (#(?a:?b)|#?a "-" #?b)
               (:?L|"," [%(expandRanges$!sjt:?L))
           )
        &   whl
          ' (   (!L:&!b|(!b,!L))
              : ?L
            & -1+!b:~<!a:?b
            )
        & !L
      |
  )
& out$(str$(expandRanges$"-6,-3--1,3-5,7-11,14,15,17-20"))