...系起来考虑;Lundgren[11](1973)和Britton[12](1980)竖立了关于乘客空间分布和旅游业的焦点—边缘理论模子(core-periphery model),他们强调了边缘区域对焦点区域的依靠。Mitchell and Lovingood[13](1976)从空间相干角度论说了城市公共游憩题目问题。
The utility model provides a trigonal pencil which consists of a pencil core and a pencil body, and is characterized in that the trigonal pencil body is arranged on the periphery of the pencil core.