### 13.5.1 Lines and directed lines in space: line

See section 12.7.1 for lines in the plane.

The line command returns and draws a directed line given one of the following types of arguments:

- Two points or a list of two points.
  The direction of the line is from the first point to the second point.
  Input:
  line([0,3,0],point(3,0,3))
  Output:
- A point and direction vector (in the form [u1,u2,u3]).
  The direction of the line is given by the direction vector.
  Input:
  line([0,3,0],[3,0,3])
  Output:
- Two equations for planes.
  The direction of the line is given by the cross-product of the normals for the planes. For example, the intersection of the planes x=y (normal (1,−1,0)) and y=z (normal (0,1,−1)) will be (1,−1,0)× (0,1,−1) = (1,1,1). Input:
  line(x=y, y=z)
  Output: