I am a beginner in lean prover and I have struggled a bit with the following example: I need to proof the following ∃ x, f x Where f is a func ...

A lot of proofs in Lean 3 were structured via the assume syntax e.g. I was unable find a similar reference section for tactics in lean 4 like in 3, ...

I'm using Lean4 in VS Code and it has the essential feature of showing me definition of anything I select. Is there some way to also find instances of ...

I see in Core.lean but there is no Or.comm to be seen. Where can I find it? ...

I noticed that both and work in the same way. Same goes when proving theorems. Are those equivalent? What is the difference between them? ...

I want to make the following I tried using the exists.elim and exists_unique.elim but i can't figure out how to use them properly, also I can't use ...

I'm trying to learn Lean. I can't understand why the last equality substitution does not work (I'm just trying to "literally" replace 0+c by a simple ...

I want to prove below goal. ring, simp, linarith is not working. Also I tried calc, but it too long. Is there any automatic command to erase common ...

If I have two functions f and g, in Haskell I can compose them by writing g.f. How do I do the same thing in Lean 4? ...

I'm just starting out with lean. Can I define define the assumptions of a theorem? For example, proving that for any integer pair min and max, every ...

Is there an infix notation that would allow to rewrite those proofs more naturally as ...

I'm just starting out with lean. Say I want to prove something about functions between two finite types. For example since there are just a few po ...

I'm trying to construct this proof in Lean: (P → Q) ∧ (R → ¬Q) → ¬(P ∧ R) It feels like a simple proof by contradiction: Assume P and R, the opposi ...

When playing the Natural Number Game (in Lean), in Advanced Multiplication World Level 2/4, I used the following code. The last three lines seem to ca ...

I want to prove the fact "A function is injective, then it has left-inverse." in Lean Prover. As you know, in standard proof of this theorem, ( https ...

I'm learning Theorem proving with Lean in Natural number game, and I have difficulty in understanding the behavior of rw tactic. In Level 1/17 in Ine ...

The List type in Lean 4's prelude has a lot of nice goodies implemented, e.g. List.map, List.join, etc. A classic example in dependently-typed langua ...

I am new to Lean 4, and I was doing the exercises from Functional Programming in Lean, in particular the one about defining a length function for a cu ...

I just got a new MacBook Air (M1, macOS 12.3.1) and installed Sage from the dmg and it's working beautifully. But now I'd like to install some other t ...

Lean 4 is a purely functional programming language, but is it lazy (like Haskell) or strict (like Idris) and what are the implications of this? Is the ...