In a given matrix below, say rows and columns are formed of {a,b,c,d}

$\begin{bmatrix}\ 1\ 0\ 0\ 0\ \\1\ 1\ 0\ 1\\1\ 1\ 1\ 1\\0\ 0\ 0\ 1\end{bmatrix}$

Then the pairs in the relation are (a,a) (b,a) (b,b) (b,d,) (c,a) (c,b) (c,c) (c,d) (d,d)
And therefore the relation is an order

Now, how do I determine the least and minimal and greatest and maximal elements? This is not so easy to me as it when a poset is in single numbers. I have the answer, but I do not know how to arrive to the answer. I should say solution.