“…, e n } is the edge set of X with a given direction, and k is a positive integer. For each edge e i ∈ E, we can give e i the partition {I (k) i,j }, 1 ≤ j ≤ j(i, k), for f k such that (1) the initial point of I (k) i,1 is the initial point of e i , (2) the terminal point of I (k) i,j is the initial point of I (k) i,j+1 for 1 ≤ j < j(i, k), (3) the terminal point of I (k) i,j (i,k) is the terminal point of e i , (4) …”