### 12.16.11 Check it two lines in the plane are parallel: is_parallel

See section 13.13.3 for checking for parallels in three-dimensional geometry.

The is_parallel command is a Boolean function which takes as argument two lines.

is_parallel returns 1 if the lines are parallel and returns 0 otherwise.
Input:

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

Output:

1

Output:

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

Output:

0