: walk ( stack point -- stack' )
    {
        [ clone [ 1 + ] change-x over push ]
        [ clone [ 1 - ] change-x over push ]
        [ clone [ 1 + ] change-y over push ]
        [ clone [ 1 - ] change-y over push ]
    } cleave ;

: (ant) ( total seen stack -- total' )
    [ dup empty? ] [
        dup pop pick dupd in? [ drop ] [
            [ pick adjoin ] keep
            dup walkable? [ [ 1 + ] 3dip walk ] [ drop ] if
        ] if
    ] until 2drop ;

: ant-no-locals ( -- total )
    0 HS{ } clone V{ } clone 1000 1000 <point> over push (ant) ;