w( "CDM" "XLC" "IVX" )
m:
    2
    step
    @0
    init
    left-uncons
    3
    copies
    inits
    tuck
    cartesian-product
    @5
    left-cons
    catenate #(list+list)
    right-cons
}
fold-product
    show-line
m1
"M"