diff --git a/README.md b/README.md
index acbec90..3ec795d 100644
--- a/README.md
+++ b/README.md
@@ -42,6 +42,8 @@ For part 2, the accessible locations are tracked, and removed individually from
 
 :mag_right: Puzzle: <https://adventofcode.com/2025/day/5>, :white_check_mark: Solver: [`Cafeteria`](src/solvers/cafeteria.rs)
 
+From the input data, we construct a [`MultiInterval`](src/common/interval.rs), which is a ordered set of integer intervals (based on a [B-tree](https://doc.rust-lang.org/std/collections/struct.BTreeSet.html)), such that all contained intervals are disjoint. With this data structure, testing for containment and determining the number of contained integers becomes trivial.
+
 ### Day 6: Trash Compactor
 
 :mag_right: Puzzle: <https://adventofcode.com/2025/day/6>, :white_check_mark: Solver: [`TrashCompactor`](src/solvers/trash_compactor.rs)