To give characterizations of the sequentially quotient,π-images and the sequentially covering, π-images of locally separable metric spaces in the notion of sieve and the following has.

Discussion on sectional mining,technical feasibility and economic rationality of steep side expansion of Guangou quarry is made and some issues to be noted are proposed due to the problems existing in the design and mining of the quarry,such as large stripping volume in the initial mining stage and voriation in stripping ratio during mining.

According to the actual situation of rib spalling in high caving face in Sihe Coal Mine,after the mechanical analyzing,this article discussed the mechanism of rib spalling,the factors which affected the spalling,and the prevention and cure measure.

Through observing and analyzing to roof and wall of spot in 6114 workface,this paper sum up rules and features of rib spalling and roof fall under complicated geology condition in sub-level caving mining workface,it raises a series of roof control measures and gets good result.