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Re:Division by zero in type theory: a FAQ by leanuser57 on Tuesday July 07, 2020 @12:29AM (#23755702)
Here is a "nonsense" theorem that is provable in Lean:

“There exists a real number r such that 1/r = 0.”

If you try to translate this theorem into maths, you will run into trouble at some point. At which point exactly depends on how you want to make things precise... which is exactly what mathematicians avoid when talking about division in fields.

Re:Division by zero in type theory: a FAQ by empath75 on Tuesday July 07, 2020 @12:44AM (#23755757)
That’s a perfectly sensible function, it’s just not ordinary division on the reals where x = 0, and you can’t use it that way.