You can visualize this figure as a tree diagram consisting of four columns of small rectangles. In the first column is <matlab>. Branching from <matlab> in the second column are two rectangles, bin and extern. There are no branches off bin. From extern there are four branches: lib, include, src, and examples. There are no branches from include and src. Branching from lib is $ARCH. Branching from examples are eng_mat, mex, mx, and refbook.