diff --git a/Cargo.toml b/Cargo.toml
index 88f7852..fe74994 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "del-geo"
-version = "0.1.20"
+version = "0.1.21"
 edition = "2021"
 authors = ["Nobuyuki Umetani <n.umetani@gmail.com>"]
 description = "2D/3D geometry utility codes"
diff --git a/src/tri3.rs b/src/tri3.rs
index 837b315..7367353 100644
--- a/src/tri3.rs
+++ b/src/tri3.rs
@@ -150,8 +150,8 @@ pub fn emat_cotangent_laplacian<T>(
 
 /// Möller–Trumbore ray-triangle intersection algorithm
 ///
-/// https://en.wikipedia.org/wiki/M%C3%B6ller%E2%80%93Trumbore_intersection_algorithm
-/// https://www.scratchapixel.com/lessons/3d-basic-rendering/ray-tracing-rendering-a-triangle/moller-trumbore-ray-triangle-intersection
+/// <https://en.wikipedia.org/wiki/M%C3%B6ller%E2%80%93Trumbore_intersection_algorithm>
+/// <https://www.scratchapixel.com/lessons/3d-basic-rendering/ray-tracing-rendering-a-triangle/moller-trumbore-ray-triangle-intersection>
 pub fn ray_triangle_intersection_<T>(
     ray_org: &[T; 3],
     ray_dir: &[T; 3],