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