eg... > 28. Divide a vertical line in two equal parts by bisecting it with a curved horizontal line that is only straight at its spot bisection of the vertica

eg... > 28. Divide a vertical line in two equal parts by bisecting it with a curved horizontal line that is only straight at its spot bisection of the vertical. I have no idea what a curved horizontal line is. A horizontal line is parallel to the X axis of the XY plane and has no curvature.