Checking whether two lines in the plane are perpendicular

See Section 27.11.4 for checking for perpendicularity in 3D geometry.

The is_perpendicular command determines whether or not two lines are perpendicular.

is_perpendicular takes two arguments: L₁,L₂, two lines.
is_perpendicular(L₁,L₂) returns 1 if L₁ and L₂ are perpendicular and otherwise returns 0.

is_perpendicular(line(0,1+i),line(i,1))

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