Trapezoidal no volume! It is a planar graph!
梯形没有体积！它是一个平面图形！
In this paper, Euler's formula and Handshaking lemma is used to obtain the face chromatic number of a planar graph by solving equations.
本文在前人研究的面着色问题基础上，运用欧拉公式和握手定理通过解方程组得到连通平面图的面色数。
Some upper bounds of the edge number for two class planar graphs are given. Some sufficient conditions for a planar graph to be class 1 are obtained through these bounds of edge number.
给出了平面图为第一类图的边数的一些上界，并给出了平面图为第一类图的一些充分条件。
Some upper bounds of the edge number for two class planar graphs are given. Some sufficient conditions for a planar graph to be class 1 are obtained through these bounds of edge number.
给出了平面图为第一类图的边数的一些上界，并给出了平面图为第一类图的一些充分条件。
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