Other predicates

[DanielVandH]

It would be useful to have adaptive versions of the following predicates

• parallelorder: This predicate is defined by parallelorder(a, b, p, q) = orient(b - a, q - p, 0) for points in the plane.
• acuteangle: Defined by

function acuteangle(p, q, r)
prx, pry = p[1] - r[1], p[2] - r[2]
qrx, qry = q[1] - r[1], q[2] - r[2]
return prx * qrx + pry * qry 
end