What is the difference between git-gc, git-repack and git-prune?

Hi!

For git-prune, according to the manual, it will delete all the dangling objects. So it is easy to understand. However, in the git-gc manpage, there is another option named "--prune". Does that make git-gc do the same thing as git-prune?

And manpage of git-gc says it cleans unnecessary files and compresses the objects, and git-repack also compresses the objects too. Are there any difference between these two operations? Or do I need to invoke git-repack after running git-gc? Thanks!

Zhenqing