Presas普雷萨斯Presabbr.主席；总统(=President)abbr.现在(=present)presbyopia/surgery老视／外科手术preservation policies数字保存政策prestressed brickwork预加应力砌砖块Prestressed cofferdam预应力围堰preselector mechanism预定位控制机构preservation of debts债的保全prestressing analysis预应力分析prestretching process预拉伸过程presumptive liability推定赔偿责任presupposition choice预设选择

1. This essentially implies that the presheaf is a sheaf.
   这实质上蕴含着预层是一个层。