Lines in the diagram are represented by a line segment with arrows on both ends. We can identify two lines in the diagram: g and h.
However, only h is intersecting the plane. We can also use any two points on a line to name it. Points P and Y are on the line, so we can also name it PY. The order of P and Y does not matter and is, therefore, an arbitrary choice. By the same principle, another name for the line h is YP.
