In many places the two things to compare are handled.
Since the original algorithm was for files, they are often referred to
as "files", and their elements as "lines", even when comparing elements
of lists or characters of strings.
A few naming conventions are used.
They can be called first/second left/right or 1/2.

If a variable ends in "1" or "2" it refers the first/second file.

"m" is the length of the first file.
"n" is the length of the second file.
"i" is usually an index in the first file.
"j" is usually an index in the second file.
