@Thomas Richard Thank you!  This is a much better way to avoid the above problem.

@acer  That might seem like a little bit more backslash.

@Carl Love  Sorry, I didn’t make it clear. I mean to remove terms containing a and exactly one other variable. But I have to say that the answers you provide later are very beautiful and practical, and sometimes they will be used. I hope you don’t delete it though they are a little bit different from what I meant here.

@Kitonum  

We may think about it a little bit more. Now we just delete "ab", "ac" and “ad” and so on. I mean all the "a*x"  forms that have "a" in them need to be deleted. Note that "x" stands for exactly one letter. For example：

s := {a*b*c, a*b*c*d, 3*a}

The above expression f is simple, so the above method can be done. But if there are many kinds of a* x in f, the codes may not be so neat.

@markweitzman  Just as the link says, the Risch algorithm is a method of indefinite integration used in some computer algebra systems to find antiderivatives. In many cases, definite and indefinite integrals are not the same difficulty.  You might think they're related because of  the Newton-Leibniz formula.  The following link is worth looking at, although the topic of discussion is Mathematica's integration problem.

https://mathematica.stackexchange.com/questions/204191/a-discontinuity-in-an-integral

@mmcdara  Thank you, I learned a lot of skills from your codes, although the effect seems not so good in the new version according to your approach, as shown in the following picture.

Maybe we can change the code to do something like this, maybe it looks a little bit better.

@Carl Love any array plot in 2021 is same bug.

@Carl Love The computer I have now only installed maple2020. It's late at night in my place, and I will run it on another computer with maple2021 installed as soon as possible tomorrow. maple2020 seems to be able to convert to latex and run your code well, but it is not displayed in the form of an array.

@Carl Love  Thank you for your correction, and sorry for the confusion caused by my English level.

Another interesting thing is that when I run the code on this post, although many pictures in eps format are generated, an error occurs when I run the latex code.

https://www.mapleprimes.com/questions/228033-How-To-Solve-The--Unreasonable-Output

graphs2.mw

@acer 

It seems that we cannot choose part of the border to be a dashed style.

@Carl Love What I mean is that it may require further programming, such as generating some special graphs. For example Chordal graphs with 10 vertices, or planar graphs. It is true that we can use the select function, but it is not efficient all the time when the number vertices are more than 10.

It seems difficult to do with the options of this function NonIsomorphicGraphs. Temporary refers to perhaps future maple can easily do.

Sorry, it seems that it can be read directly.

I have always wanted to open it and have a look so I can select some graphs to read. 

I found that copy them and  paste to notepad++. Each data is starting to form a separate row again, which is strange.

@tomleslie Thank you very much for your patient guidance!

@tomleslie Thank you very much for your help. A single graph data in a text, run your code, great! But  If my data is all in one file, it seems that there will be some problems. The file is attached below:
graphdata.txt

I have very limited experience with text processing. Can you help me deal with it? I will learn a lot of relevant knowledge. Thanks!