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Nemocas / AbstractAlgebra.jl

Generic abstract algebra functionality in pure Julia (no C dependencies)
https://nemocas.github.io/AbstractAlgebra.jl/dev/index.html
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Difference between `inverse_image_fn` and `inverse_fn` ? #1123

Open fingolfin opened 2 years ago

fingolfin commented 2 years ago

Consider the following undocumented methods:

inverse_image_fn(f::Map(ModuleIsomorphism)) = f.inverse_image_fn
inverse_fn(f::MapWithSection) = image_fn(f.section)
inverse_fn(f::MapWithRetraction) = image_fn(f.retraction)

Are there any conceptual differences here? Or could/should inverse_image_fn be renamed to inverse_fn?

wbhart commented 2 years ago

The first has nothing to do with the map interface. It's an internal undocumented function. You can rename it if you want, but I am not even sure I remember what it does.

wbhart commented 2 years ago

When I did the modules, Claus had this thing he was calling a preimage, which wasn't actually mathematically strictly a preimage. So I remember implementing that for him because he wanted it right when I finally finished modules. Maybe this had something to do with that.

In the module docs is preimage which I presume is the real thing (though it gives a "preimage" at a point, not a set theoretic one).