EdgeAdd[g, e] 通过把边 e 添加到图 g 生成图.
EdgeAdd[g, {e1, e2, ...}]对 g 添加一组边.
对图添加一条边：
EdgeDelete VertexAdd DirectedEdge UndirectedEdge
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或者 UndirectedEdge[v, w] 指定一条无向边. 
或者 DirectedEdge[{v, w}] 指定一条有向边.
或者 UndirectedEdge[v, w] 指定一条无向边. 或者 DirectedEdge[{v, w}] 指定一条有向边.