OpengGL insights book question

I just started reading this book, but as soon as I start reading the second example it talks about an Angel.h header.
Where can I find it? I didn’t understand what I should do with that and even trying to copy paste the cope doesn’t solve anything.
Anyone can help?

I haven’t got the book could it be from

Nope! The article referred to is written by Prof. Edward Angel, and it is his own header used in all examples in the book “Interactive Computer Graphics, A top-down approach with OpenGL (Sixth Edition)”. The first two chapters in the OpenGL Insights book are aimed for teachers, just to illustrate how OpenGL teaching can be organized, and there is no accompanying code on the “OpenGL Insights” site.

The header (you think) you need can be downloaded from the following address Angel.h, but for the example it is totally irrelevant.

But if it is totally irrelevant, than why did he actually use the header file?
And that happens on other books too on OpenGL

If you took a look at that header file, you would see it includes support for math, GL, glew, glut, defines some constants etc. The file is actually useful for the project from where the code has been taken, but it is irrelevant for the example in the book. OpenGL Insights is not a guided tutorial, it is rather a collection of articles.

Thanks, your reply greatly helped!