如果知道了，向量空间在单连通区域内处处有定义，那么就可以毫无顾忌地，在这个区域里使用格林公式了？
Well, if you know that your vector field is defined everywhere in a simply connected region, then you don't have to worry about this question of, can I apply Green's theorem to the inside?
全空间去掉原点，它是单连通的吗？
OK, so space with the origin removed, OK, you think it's simply connected?
他在1904年就提出猜想：在四维空间，所有单连通的封闭三维面都能转化为一个三维球体。
His conjecture, made in 1904, was that in this four-dimensional world, all closed three-dimensional surfaces that are simply connected could be transformed to look like a three-dimensional sphere.
应用推荐