Confusion with modules in Rust when having main.rs and lib.rs

Hello! I'm new to Rust and trying to understand the module system. I have a project that I created with `cargo new my_project`. Inside, there are two files: `main.rs` and `lib.rs`. I thought I could just declare a module in one of them and use it in the other, but nothing works. Here's my structure: ``` my_project/ ├── Cargo.toml ├── src/ │ ├── main.rs │ └── lib.rs ``` I want to define a function in `lib.rs` and call it from `main.rs`. I tried writing in `lib.rs`: ```rust mod utils { pub fn greet(name: &str) -> String { format!("Hello, {}!", name) } } ``` And in `main.rs`: ```rust mod utils; use utils::greet; fn main() { println!("{}", greet("Alice")); } ``` But the compiler gives an error: `error[E0432]: unresolved impo