If there are even lines on a point, then the point is an even point.

The key to judge whether a figure can be drawn in one stroke is to look at the number of singularities:

When there are zero or two singularities (there can't be one, and the singularities all appear in pairs), they can be drawn with one stroke, and vice versa.

Extended data

Through the long-term observation of the content of modeling and lines with different properties, the author injects the author's emotion and forms it in one breath, showing the overall form of the whole content.

Because the overall form of a stroke is a stroke of Chinese painting, one stroke is considered as a unique writing method of Chinese painting. A figure composed of a stroke is called a stroke, and there are related games and books.

The most famous mathematical problem is the seven-bridge problem (Euler solution). The concept of a stroke is to discuss whether a figure can be drawn with one stroke. Any endpoint in a graph is divided into singular points and even points according to the number of connecting lines.

Only figures with even points and figures with only two singularities can draw strokes. A graph with only even points has no starting point, and two singularities must start from one point and end at the other. In any graph, singularities appear in pairs, and there is no graph with odd points.

1. Any connected graph composed of even points can be drawn with one stroke. When drawing, you can start from any even point, and finally you can finish drawing with this point as the end point.

3. Any connected graph with only two singularities (the rest are even points) can be drawn with one stroke. When drawing, one singularity must be the starting point and the other singularity must be the end point.

[14] Other situations cannot be brushed aside. Divide the odd number by two and work out how many strokes are needed to draw this picture. )

References:

A stroke (name of mathematical question type)-Baidu Encyclopedia