Beginning, Middle, End

How many ways can you divide up a chain?
What is the middle of 1,2,3?
Where is almost to the end of 1,2,3,4?
The "beginning, middle, end Markov algorithm" works on short sequences.
What letter is at 25% of the alphabet?
A little harder?
The invariant representation for alphabet is built from sub invariant representations for the alphabets sub-sequences. You are only able to compare lengths of certain invariant representations chains at face value. Changing focus, putting on a short term memory stack and moving lower or higher in the representation hierarchy facilitates chain and element comparisons.