A digraph D(V, E) is said to be graceful if there exists an injection f : V (D) → { 0, 1, ·· , |E|} such that the in-duced function f' : E(D) → { 1, 2, ··· ,|E|} which is defined by (u, v) = [f (v) — f(u)] (mod (|E| + 1)) for every directed edge (u, v) is a bijection. Here, f is called a graceful labeling(graceful numbering) of digraph D(V, E), while f' is called the induced edge's graceful labeling of digraph D(V, E). In this paper, we discuss the gracefulness of the digraph n — and prove the digraph n - C_(17) is graceful for even n.
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机译：如果存在注入f：V（D）→{0，1，··，| E |}使得归纳函数f'：E（D），则有向图D（V，E）被认为是优美的。 ）→{1，2，···，| E |}，对于每个有向边，其定义为（u，v）= [f（v）-f（u）]（mod（| E | + 1）） （u，v）是双射。在此，f被称为有向图D（V，E）的优美标注（优美编号），而f'被称为有向图D（V，E）的诱导边缘优美的标示。在本文中，我们讨论了有向图n的优美性，并证明了有向图n-C_（17）对于n也很优美。
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