an eraser is a kind of solid
blackboard_eraser is not eraser. ink_eraser is eraser. blackboard_eraser is eraser. one_type_of_eraser is rubber_erase. rubber_eraser is eraser. one_type_of_eraser is not rubber_erase. eraser is not implement. ink_eraser is not eraser. eraser is implement. rubber_eraser is not eraser.