### 26.15.11 Checking whether two lines in the plane are parallel

See Section 27.11.3 for checking for parallels in 3D geometry.

The is_parallel command determines whether or not two lines are parallel.

- is_parallel takes two arguments: L1,L2, two lines.
- is_parallel(L1,L2) returns 1 if L1 and L2 are parallel and otherwise returns 0.

#### Examples

is_parallel(line(0,1+i),line(i,-1))

1 |  |  |  |  |  |  |  |  |  |

is_parallel(line(0,1+i),line(i,-1-i))

0 |  |  |  |  |  |  |  |  |  |