Flakes: what does ∅ -> ε mean? (big bundle of questions)

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1

I have created a directory flake that contains a binary.
I am installing it imperatively using nix profile install /tmp/cool-thing.

When I run nix profile history I see symbols:

Version 14 (2021-11-30) <- 13:
  path:/tmp/cool-thing#defaultPackage.x86_64-linux: ε -> ∅

Version 15 (2021-11-30) <- 14:
  path:/tmp/cool-thing#defaultPackage.x86_64-linux: ∅ -> ε

  1. What do these pairs of symbols mean?

  2. Also, what does each individual symbol signify? Guessing, they look like mathematical notation from set theory.

rambling UX feelings

I am wondering aloud at why the UX encodes meaning using mathematical notation. I love the clarity of such notation. But I worry that other users may find it off putting (e.g. obscure, too complex).

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2

One is “not installed” and one is “unknown or empty version”.

So this is transitioning from not installed to an unknown version and uninstalling again.

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3

I found the following manual page: nix store diff-closures - Nix Reference Manual

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4

Great answers. Thanks.

For the future maybe this will help to search documentation:

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