mower is a surface of light matter
power_lawn_mower is lawn_mower. power_lawn_mower is not lawn_mower. hand_mower is not lawn_mower. power_mower is not lawn_mower. aluminum is light_metal. riding_mower is power_mower. mowing_grass has linear_complexity power_mower is lawn_mower. hand_mower is lawn_mower. mowing_grass has not linear_complexity