XOR function, what was it doing, coding with XOR

Hello!

Please, if we have A1=h;
ascii(DEC)=72;
B1=G;
ASCII(dec)=103;
R1=/;
ASCII(dec)=47

These are just data I wrote out of the table.
So, we know that A1=H and that B1=g
There are 20 values for A (A1 to A20) and 20 values for B (B1 to B20).

A H
B g
R /

Each value has ascii code.
A1 has ascii code 72 (for H), B1 has ascii code 103 (for g) and R1 has ascii code 47, hich is for /.

OK.
R is short for RESULT.
A values has been coded, using function XOR.
The rule was:
(A XOR B) XOR B ==A

My question is: How to read this formula, what does it clearly mean, and how do we get R from A and B using it.
In other words: what is acutally happening here.

Many thanks!

Find here information about XOR in calc:
http://nabble.documentfoundation.org/libreoffice-l10n-XOR-formula-td4028297.html