Checking if two lines in the plane are parallel: is_parallel

### 13.16.11 Checking if two lines in the plane are parallel: is_parallel

See Section 14.13.3 for checking for parallels in three-dimensional 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

- Input:
  is_parallel(line(0,1+i),line(i,-1))
  Output:

  1

- Input:
  is_parallel(line(0,1+i),line(i,-1-i))
  Output:

  0