Example from Hunt and McIlroy, “An Algorithm for Differential File Comparison.”
https://www.cs.dartmouth.edu/~doug/diff.pdf

-- old --
a
b
c
d
e
f
g
-- new --
w
a
b
x
y
z
e
-- diff --
diff old new
--- old
+++ new
@@ -1,7 +1,7 @@
+w
 a
 b
-c
-d
+x
+y
+z
 e
-f
-g