Display dependencies and reverse dependencies for each package?

[fingolfin]

We show a page for each GAP package on the website with some information on it.

Perhaps we should also show for each package

• its required dependencies (with a link to that package)
• its optional dependencies
• its "reverse dependencies" / "dependants" / packages depending on it (directly)

That may be helpful for some people. Other language package manager do it, e.g.

• https://juliahub.com/ui/Packages/General/GAP
• https://cran.r-project.org/package=evitaicossa (but without the dependants)

[olexandr-konovalov]

Cf. also #29