# EKF Slam algorithm doubt at observation update

I have some doubt on EKF Slam with known correspondence in the measurement update state. I follow the algorithm from Probabilistic Robotics by Sebastian THRUN. This Algorithm is on Chapter 10 page No:249 of this books.

I attached a snapshot of my doubt.

In this algorithm line No: 10 and 12 create some doubts.

I want to know what is $\bar\mu_{t,x}$ and $\bar\mu_{t,y}$.

As per my understanding, it is the robot position in the given timestamp when it sees landmarks.

But I have some confusion, so it would be very helpful for me if anyone could clarify line 10,12.