diff --git a/day3/Cargo.lock b/day3/Cargo.lock
new file mode 100644
index 0000000..bdc4aa0
--- /dev/null
+++ b/day3/Cargo.lock
@@ -0,0 +1,181 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
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+dependencies = [
+ "rustc_version",
+]
diff --git a/day3/Cargo.toml b/day3/Cargo.toml
new file mode 100644
index 0000000..f25aa98
--- /dev/null
+++ b/day3/Cargo.toml
@@ -0,0 +1,23 @@
+[package]
+name = "day3"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[profile.release]
+opt-level = 3
+lto = "fat"
+codegen-units = 1
+strip = true
+
+[profile.prof]
+inherits="release"
+strip = false
+
+
+[dependencies]
+color-eyre = { version = "0.6.2", default-features = false }
+lazy_static = "1.4.0"
+linebuffer = { path = "/home/avril/work/linebuffer" }
+smallmap = "1.4.0"
diff --git a/day3/src/ext.rs b/day3/src/ext.rs
new file mode 100644
index 0000000..4f1dede
--- /dev/null
+++ b/day3/src/ext.rs
@@ -0,0 +1,32 @@
+//! Extensions
+use super::*;
+use std::{
+    iter::{self, Fuse,}
+};
+pub trait TaekTwoExt: Iterator
+{
+    fn take_two(self) -> TakeTwo<Self>;
+}
+
+#[derive(Debug, Clone)]
+pub struct TakeTwo<I: ?Sized + Iterator>(I);
+
+impl<T, I: Iterator<Item=T> + ?Sized> Iterator for TakeTwo<I>
+{
+    type Item = (T, Option<T>);
+    #[inline] 
+    fn next(&mut self) -> Option<Self::Item>
+    {
+	let first = self.0.next()?;
+	Some((first, self.0.next()))
+    }
+}
+
+impl<I: Iterator> TaekTwoExt for I
+where I: Iterator + Sized
+{
+    #[inline] 
+    fn take_two(self) -> TakeTwo<Self> {
+	TakeTwo(self)
+    }
+}
diff --git a/day3/src/main.rs b/day3/src/main.rs
new file mode 100644
index 0000000..7aec75a
--- /dev/null
+++ b/day3/src/main.rs
@@ -0,0 +1,117 @@
+
+#[macro_use] extern crate lazy_static;
+
+use smallmap::{
+    Map,
+    smallmap,
+};
+use std::{
+    collections::BTreeSet,
+};
+use linebuffer::{
+    buf::forward,
+    TryFromBuf,
+    FromBuf,
+    ParsedLines,
+};
+
+use color_eyre::{
+    eyre::{
+	self, eyre,
+	WrapErr as _,
+    },
+    Help as _, SectionExt as _,
+};
+
+mod ext;
+pub use ext::*;
+
+fn init() -> eyre::Result<()>
+{
+    color_eyre::install()
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
+struct Sack {
+    split_by: usize,
+    containers: Vec<BTreeSet<char>>,
+    full: BTreeSet<char>,
+}
+
+impl Sack
+{
+    /// Compute the intersection of each `N` part of the container
+    pub fn intersection(&self) -> impl Iterator<Item = char> + '_
+    {
+	self.containers.iter().take_two().flat_map(|(a, b)| b.map(move |b| (a, b)))
+	    .map(|(a, b)| a.intersection(b)).flatten().copied()
+    }
+}
+
+#[inline] 
+fn read_input_from<R: std::io::Read>(input: R) -> ParsedLines<R, forward::FromStr<Sack>>
+{
+    ParsedLines::new(input)
+}
+
+fn read_input() -> eyre::Result<ParsedLines<impl std::io::Read + 'static, forward::FromStr<Sack>>>
+{
+    let reader = std::fs::OpenOptions::new()
+        .read(true)
+        .open("input")
+        .wrap_err("Failed to open input file for reading")?;
+    Ok(read_input_from(reader))
+}
+
+#[derive(Debug)]
+pub struct SackParseError{
+    expected_div: usize,
+    size: usize,
+}
+
+impl std::str::FromStr for Sack
+{
+    type Err = SackParseError;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+	let (first, second) = s.split_at(s.len()/2);
+	Ok(Self {
+	    split_by: 2,
+	    containers: vec![
+		first.chars().collect(),
+		second.chars().collect(),
+	    ],
+	    full: s.chars().collect(),
+	})
+    }
+}
+
+#[inline] 
+fn prop_swivle<'a>(sigh: impl IntoIterator<Item = char>+ 'a) -> impl Iterator<Item = usize> + 'a
+{
+    lazy_static! {
+	static ref PMAP: Map<char, usize> = ('a'..='z').enumerate().map(|(i, n)| (i+1, n))
+	    .chain (('A'..='Z').enumerate().map(|(i, n)| (i + 27, n)))
+	    .map(|(i, n)| (n, i))
+	    .collect();
+    }
+    sigh.into_iter().map(|ref ch| PMAP.get(ch)).flat_map(std::convert::identity).copied()
+}
+
+fn main() -> eyre::Result<()> {
+    init().wrap_err("Panic hook failed to install")?;
+
+    let mut input = read_input()?;
+    
+    let mut psum = 0;
+    
+    while let Some(sack) = input.try_next()
+    {
+	let sack = sack.expect("Failed to parse input line");
+	psum += prop_swivle(sack.intersection())
+	    .sum::<usize>();
+	// TODO: part2: find sack.full's intersection through *all other* lines, up to two where the intersection is exactly 1 between all three. This is boring, I give up.
+    }
+    println!("{psum}");
+    
+    Ok(())
+}