Very annoyed that the FSF kept changing its links over the years, without redirect.
there's 〈Introduction to Programming in Emacs Lisp〉 at 〔http://www.gnu.org/software/emacs/emacs-lisp-intro/〕
now that link is dead.
new one is at https://www.gnu.org/software/emacs/manual/eintr.html
A decade ago, i have lots links to FSF's elisp doc. Then, it went dead, then reported the bug, and it got fixed, then went dead again. This went on twice. That's when i finally decided to mirror it on my site (info "(elisp) index") and stop linking to FSF.
So, if you link to FSF in your blog, you want to check every year if it is still good.