1. Depend upon Abstractions. Do not depend upon concretions. 依赖抽象,不要依赖具体。
2. The invention can be used for mining low coal seams containing other concretions, ordinary low coal seams, medium-thickness coal seams and high coal seams. 在含其它结核的薄煤层、普通薄煤层以及中厚、厚煤层同样可以采用。