http://www.numbertheory.org/book/mp103.pdf
On page 12 of the book I'm stumped.

It says that the 'column numbers in which the leading entries 1 occurs' are denoted by $\displaystyle c_1,c_2,...c_r$, where r is the number of nonzero rows.

They give an example, where r=3, which means there are 3 non-zero rows in the matrix (as far as I can tell). Then the give some values for the c's. I undersatnd how the obtained the first 3 values:

$\displaystyle c_1=2$,$\displaystyle c_2=4$,$\displaystyle c_3=5$.

However, I don't see how they obtained values for $\displaystyle c_4,c_5$ and $\displaystyle c_6$.