## Stream: general

### Topic: Proof examples?

#### Ryan Smith (Sep 21 2018 at 04:46):

Hi, I'm entirely new to lean. I've read the docs, but I'm struggling to see what it would look like to prove anything in practice. The homepage didn't have much of a gallery, do we have examples of what a simple proof of the infinitude of primes or Lagrange's theorem for finite groups would look like?

#### Bryan Gin-ge Chen (Sep 21 2018 at 04:51):

You may want to check out the lean mathlib project; many of the contributors are quite active in this chat. Here's the proof of the infinitude of primes in mathlib, and here's the proof of Lagrange's theorem.

#### Mario Carneiro (Sep 21 2018 at 04:53):

Yay, mathlib already contains two theorems selected at random from math. Thus, mathlib has 75% of math, QED

#### Johan Commelin (Sep 21 2018 at 04:53):

Welcom @Ryan Smith If you want you can write a little introduction about your background in https://leanprover.zulipchat.com/#narrow/stream/113489-new-members/subject/Introductions. We're a bunch of enthousiastic mathematicians and computer scientists trying to build a library of data structures, automation and of course a bunch of mathematics.

#### Bryan Gin-ge Chen (Sep 21 2018 at 04:53):

I also forgot to say welcome! I'm also fairly new to lean and I've been asking silly questions in the #new members stream for the past month or so.

#### Johan Commelin (Sep 21 2018 at 04:54):

Since a couple of weeks we try to post in https://leanprover.zulipchat.com/#narrow/stream/116395-maths/subject/What's.20new.20in.20Lean.20maths.3F to tell people about new stuff in the library

#### Mario Carneiro (Sep 21 2018 at 04:55):

Johan, could you summarize the results of the kbb project in that thread?

#### Johan Commelin (Sep 21 2018 at 04:56):

I will try :smiley:

#### Simon Hudon (Sep 21 2018 at 04:58):

Btw, why is that thread in #maths ? That's a stream I don't follow

#### Ryan Smith (Sep 21 2018 at 05:00):

Oh cool, a number of basic primitives are already implemented. I thought things were a bit more rudimentary from reading the documentation.

#### Johan Commelin (Sep 21 2018 at 05:12):

@Simon Hudon Because it really is about What's new in maths in Lean. We could probably have a similar thread in general where we post about new tactics and data structures and so on. But that thread is really about "Yeah, we have the fact that quotients of Noetherian modules are Noetherian!".

#### Johan Commelin (Sep 21 2018 at 05:13):

Also see my latest post there :wink:

#### Simon Hudon (Sep 21 2018 at 05:15):

The one summarize Kevin's birthday present?

Right, that one.

#### Johan Commelin (Sep 21 2018 at 05:16):

Is that the kind of stuff you would be interested in to know?

#### Simon Hudon (Sep 21 2018 at 05:20):

I think I misread, I thought you also announced tactics there (like linarith). To be frank, I didn't understand too much of what was put in Kevin's present.

#### Johan Commelin (Sep 21 2018 at 05:21):

We also announced linarith there. So there might be some overlap... but I think we could cross post those announcements to a "What's new in Lean thread in #general"

#### Simon Hudon (Sep 21 2018 at 05:22):

That sounds like a good idea. Thanks :)

#### Mario Carneiro (Sep 21 2018 at 05:28):

I cross posted abel there since there is an overlap of interest, but also because people always want to have a conversation about these news items and I would rather not clutter up an announcement thread with that

#### Mario Carneiro (Sep 21 2018 at 05:30):

In fact, I suggest we get in the habit of linking each news item to a thread about it specifically so people can use it as a hub

#### Johan Commelin (Sep 21 2018 at 05:39):

Done.

Last updated: Dec 20 2023 at 11:08 UTC