Regarding page $171$ of CLRS $3$rd edition, which line is the exact beginning of the iteration for the PARTITION procedure? I guess I understand the basic idea of the PARTITION procedure from the book "Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest and Clifford Stein. Introduction to Algorithms, 3rd Edition. The MIT Press, 2009"

since I've answered the exercises for section $7.1$ correctly on my own.
However, the comments for Figure $7.1$ confuses me somehow.

for example, the book says

(b) The value $2$ is “swapped with itself”

which seems to indicate part (b) of the figure corresponds to the first iteration ($guess_1$).
However, the variable j right above the $2$nd position indicates $j=p+1$, which, in turn, indicates it's the second iteration, if the exact beginning of a loop starts at line 3 ($guess_2$). This is in contradiction with $guess_1$.
Another explanation could be that, the exact beginning of the iteration starts at line 4, immediately after for j = p to r - 1. Should I go with this?
 A: 
(a) The initial array and variable settings. None of the elements have been placed in either of the first two partitions.
(b) The value $2$ is “swapped with itself” and put in the partition of smaller
values.

(a) refers to the first time the program has run to line 4. At that moment, i == p - 1 and j == p.
(b) refers to the second time the program has run to line 4. At that moment, i == p and j == p + 1. The value $2$ has been "swapped with itself". The value $2$ has been put in the partition of smaller values. That action of swapping and putting happened at line 5 and 6 of the previous iteration of the for loop, when the value of j was still p.
Please note "is swapped" in "the value $2$ is..." describes the current state of the value $2$. It does not indicate what will happen next.
It might have been clearer had it been written as "the value $2$ has been swapped... and has been put...". 

The selection of the moments that are explained by the textbook lets you view the state of the array and the tracking indices right at the moment of the comparison between the element on the focus and the pivot. That comparison is the key step to implement partition.
Of course, each iteration of the for loop starts at line 3 and ends when the block of line 4, 5 and 6 ends, except the last iteration. It is indeed slightly confusing that each part of (a), (b), etc. does not correspond to exactly one or more whole iterations. 
