Wanted: Simple ring signature example
Here is an explanation of step 4.
Look at Figure 2 of the paper.
Lets say $y_s$ is $y_3$ at 6 o'clock.
Start at 12 o'clock and calculate going clockwise until you arrive at 6 o'clock. Denote the result by $r$.
Start again at 12 o'clock and calculate going counter-clockwise until you arrive at 6 o'clock. Denote the result by $l$.
Now $l =r \oplus y_s$, which gives the solution $y_s =r \oplus l$.