MetaChat is an informal place for MeFites to touch base and post, discuss and
chatter about topics that may not belong on MetaFilter. Questions? Check the FAQ. Please note: This is important.
Senyar, it's a plain substitution cypher (like the the list of A-Z alphabets represented by a set of a/b values) but he tries to hide the fact that it's "a" or "b" by saying, let A or B be anything like A is one type of note and B is another type of note.
It's basically a very weak encryption format that takes advantage of being hidden / not obviously coded
lol. Substitution cyphers are very simple (it's so old and weak it's known as the Caesarian Shift after Julius Caesar) but yeah you have to get into a certain frame of mind to figure it out as a newcomer to the concept