    distanceF cxs xs = max 0 $ (disctance2 xs cxs)
instance Figure Point where
    distanceF cxs (Point xs) = max 0 $ (disctance2 xs cxs)
instance Figure Sphere where
    distanceF cxs (Sphere xs r _) = max 0 $ (disctance2 xs cxs - r)