Let N be the set of all positive integers.

设N是全体正整数的集合。

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In particular, some upper bounds of the vertex arboricity of the integer distance graph G(Z, D) are obtained when D is a set of positive integers and Z the set of all integers.

特别地，当D是某正整数集合，Z是整数集时，得出了整数距离图G（Z ，D）的点荫度的几个上界。

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If the set is small, we can simply list the members and number the list with positive integers, starting with 1 and proceeding in the natural order until we reach the end of the list.

如果集合较小，我们可以简单地列出起成员并用正整数记录列出的成员的数目，从1开始，以自然数的次序往下直至结束。

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