Arrow style

Stream: mathlib4

[Ruben Van de Velde]

Do we have a style guideline / linter that says to use ← rather than <-?

[Michael Rothgang]

No linter, I believe --- not sure about the style guide. The former is relative easy once the latter exists :-)

[Bhavik Mehta]

I think we should add a preference for ← over <- to the mathlib style guide

[Michael Rothgang]

Right now, mathlib doesn't have any occurrences of <- for this purpose.

[Michael Rothgang]

Do we want to lint the same for ->? (We have a few hundred of these, but search-replace should deal with those quickly.)