Cut ray tracing fancy

Author: trevordblack

books/RayTracingInOneWeekend.html

@@ -396,8 +396,7 @@
 $\vec{\mathbf{b}}$ is the ray direction. The ray parameter $t$ is a real number (`double` in the
 code). Plug in a different $t$ and $p(t)$ moves the point along the ray. Add in negative $t$ and you
 can go anywhere on the 3D line. For positive $t$, you get only the parts in front of $\mathbf{a}$,
-and this is what is often called a half-line or ray. This is where the _ray_ in
-_ray tracing_ comes from.
+and this is what is often called a half-line or ray.
 
   ![Figure [lerp]: Linear interpolation](../images/fig.lerp.jpg)