diff --git a/Cargo.lock b/Cargo.lock
index 2e12759..54bb767 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -197,6 +197,16 @@ dependencies = [
  "nom",
 ]
 
+[[package]]
+name = "day09"
+version = "0.1.0"
+dependencies = [
+ "aoc",
+ "color-eyre",
+ "nom",
+ "rayon",
+]
+
 [[package]]
 name = "either"
 version = "1.9.0"
diff --git a/Cargo.toml b/Cargo.toml
index 6fec940..4f812a4 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,5 +9,6 @@ members = [
     "day04",
     "day05",
     "day06",
+    "day09",
 ]
 
diff --git a/day09/Cargo.toml b/day09/Cargo.toml
new file mode 100644
index 0000000..4fa788b
--- /dev/null
+++ b/day09/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "day09"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+aoc = { path = "../aoc" }
+color-eyre = "0.6.2"
+nom = "7.1.3"
+rayon = "1.8.0"
diff --git a/day09/src/bin/day09a.rs b/day09/src/bin/day09a.rs
new file mode 100644
index 0000000..c23c2b5
--- /dev/null
+++ b/day09/src/bin/day09a.rs
@@ -0,0 +1,39 @@
+// Copyright (C) 2023 Leandro Lisboa Penz <lpenz@lpenz.org>
+// This file is subject to the terms and conditions defined in
+// file 'LICENSE', which is part of this source code package.
+
+use rayon::prelude::*;
+use std::io::{stdin, BufRead};
+
+use day09::*;
+
+fn diffs(nums: &[i64]) -> Vec<i64> {
+    nums.par_windows(2).map(|l| l[1] - l[0]).collect()
+}
+
+fn calc_next(nums: &Vec<i64>) -> i64 {
+    let mut lastsum = nums[nums.len() - 1];
+    let mut currdiff = diffs(nums);
+    while !currdiff.par_iter().all(|n| n == &0) {
+        lastsum += currdiff[currdiff.len() - 1];
+        currdiff = diffs(&currdiff);
+    }
+    lastsum
+}
+
+fn process(bufin: impl BufRead) -> Result<i64> {
+    let input = parser::parse(bufin)?;
+    Ok(input.par_iter().map(calc_next).sum())
+}
+
+#[test]
+fn test() -> Result<()> {
+    assert_eq!(process(EXAMPLE.as_bytes())?, 114);
+    Ok(())
+}
+
+fn main() -> Result<()> {
+    color_eyre::install()?;
+    println!("{}", process(stdin().lock())?);
+    Ok(())
+}
diff --git a/day09/src/lib.rs b/day09/src/lib.rs
new file mode 100644
index 0000000..2a3e3f2
--- /dev/null
+++ b/day09/src/lib.rs
@@ -0,0 +1,32 @@
+// Copyright (C) 2023 Leandro Lisboa Penz <lpenz@lpenz.org>
+// This file is subject to the terms and conditions defined in
+// file 'LICENSE', which is part of this source code package.
+
+pub use color_eyre::{eyre::eyre, Result};
+
+pub const EXAMPLE: &str = "0 3 6 9 12 15
+1 3 6 10 15 21
+10 13 16 21 30 45
+";
+
+pub mod parser {
+    use aoc::parser::*;
+
+    // use super::*;
+
+    fn line(input: &str) -> IResult<&str, Vec<i64>> {
+        let (input, nums) = multi::separated_list1(character::space1, character::i64)(input)?;
+        let (input, _) = character::newline(input)?;
+        Ok((input, nums))
+    }
+
+    pub fn parse(mut bufin: impl BufRead) -> Result<Vec<Vec<i64>>> {
+        aoc::parse_with!(multi::many1(line), bufin)
+    }
+}
+
+#[test]
+fn test() -> Result<()> {
+    assert_eq!(parser::parse(EXAMPLE.as_bytes())?.len(), 3);
+    Ok(())
+}