Hello Schwalbenkoenig,
It's not that I don't think it is not Helevetica. I just had the impression that it was a very concrete variety of it. My point is that the way the type is set on the inner pages of the book is not, at least to me, very aesthetically pleasing. You can see it for yourself using the link that I mentioned in my comment to kthomps5.
Anyway, thank you for your time and help.