In principle, questions tagged resource-recommendation that do little more than provide a link should be deleted like any other (almost) link-only answer, but is it really so? If we look at most answers to, e.g., the super-question Book recommendations, we see that most of them have a simple one-paragraph description and a link, which indeed seems fine for the purpose.
As a concrete case, recently a resource-recommendation answer was deleted on the basis of being link-only (this, for those who can see it):
[user207599] Here is a Kerr metric derivation method by using ellipsoid coordinate transformation. https://academicjournals.org/journal/IJPS/article-full-text-pdf/AEE776964987
While similarly long answers to the same question have been left alone, namely:
[Robin Ekman] The original reference is Kerr, R.P. Gravitational field of a spinning mass as an example of algebraically special metrics. Phys. Rev. Lett. 11, 237.
[Mohamed IBrahim] you can also read this paper , it is very useful A Possible Intuitive Derivation of the Kerr Metric in Orthogonal Form Based On Ellipsoidal Metric Ansatz.
[Paul Masson] I'm surprised no one mentioned Chapter 6 of Chandrasekhar's Mathematical Theory of Black Holes. Then again, I personally found his derivation so opaque that I wrote my own de novo derivation in Boyer-Lindquist coordinates using the Cartan formalism.
[fazlay ahmed] i think if we follow the Ray D' Inverno book intitled Introducing Einstein Relativity then we get easily this metric. on chapter 19 it is explanied in a very simple method
So should all these four answer be also deleted as being link-only? One of them has 4 upvotes, two have 1.
A closely-related point: the policy for resource recommendations states that:
If you come across an old recommendation post, move all of the answers that are against policy into a community wiki list answer, and give it the following banner [...]
This answer is from Aug 5 '13, so "old" means earlier than that?
In summary, my questions are:
- Is the link-only policy loosened for resource-recommendation questions?
- We should only agglutinate link-only resource-recommendation answers if older than Aug 2013?