[ ScanAdj
    [ Just
        ( Word "empty" )
    ]
    ( Marker "empty" )
, ScanNoun
    [ Just
        ( Word "function" )
    ]
    ( Marker "function" )
, ScanVerb
    [ Just
        ( Word "converges" )
    , Just
        ( Word "to" )
    , Nothing
    ]
    ( Marker "converges" )
]