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> If RAR encounters a file ten times, it will compress once and store it and nine pointers.

A bunch of compression formats do that. Even zip files can, which leads to interesting tricks like:

Handling multiple identical files is certainly desirable - but this is not the "core" compression algo. Its a cute optimization trick...

> "lzma and zstd guis i've tested will store ten compressed copies"

It depends on dictionary size, word size, the actual data etc.