樹是一個沒有迴路的連接圖。而4-caterpillar是一種樹，它擁有單一路徑連接到數個長度為3的路徑的端點。一個有n個邊的無向圖G的優美標法是一個從G的點到{0,1,2,...,n}的一對一函數，使得每一個邊的標號都不一樣，其中，邊的標號是兩個相鄰的點的編號差的絕對值。在這篇論文當中，我們最主要的目的是使用一個演算法來完成4-caterpillars的優美標法。

A tree is connected acyclic graph. A 4-caterpillar is a tree with a single path only incident to the end-vertices of paths of length 3. A graceful labelling of an undirected graph G with n edges is a one-to-one function from the set of vertices of G to the set {0,1,2,...,n} such that the induced edge labels are all distinct, where the edge label is the difference between two endvertex labels. In this thesis, our main purpose is to use an algorithm to yield graceful labellings of 4-caterpillars.

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