restriction. Implicit schemes do not have this restriction for stability, but
they become inaccurate if the time step is too large.
-This condition was first recognized by Courant, Friedrichs, and Levy — in
-1943, long before computers become available for numerical computations! In
-the program, we will refine a square $[-1,1]$ seven times uniformly, giving a
-mesh size of $h=\frac 1{64}$, which is what we set the time step to. The fact
-that we set the time step and mesh size individually in two different places
-is error prone: it is too easy to refine the mesh once more but forget to also
-adjust the time step. @ref step_24 "step-24" shows a better way how to keep
-these things in synch.
+This condition was first recognized by Courant, Friedrichs, and Levy —
+in 1943, long before computers become available for numerical computations!
+Consequently, the condition on the time step is most frequently just referred
+to as the <i>CFL</i> condition. In the program, we will refine a square
+$[-1,1]$ seven times uniformly, giving a mesh size of $h=\frac 1{64}$, which
+is what we set the time step to. The fact that we set the time step and mesh
+size individually in two different places is error prone: it is too easy to
+refine the mesh once more but forget to also adjust the time step. @ref
+step_24 "step-24" shows a better way how to keep these things in synch.
<h3>The testcase</h3>