public AngleBetween__Rtype__()
        {
            var rnd = new RandomSystem(1);

            A.SetByIndex(i => rnd.Uniform__v3rt__Direction());
            angles.SetByIndex(i => rnd.Uniform__Rtype__() * (__rtype__)Constant.Pi);
            B.SetByIndex(i =>
            {
                __v3rt__ v;
                do
                {
                    v = rnd.Uniform__v3rt__Direction();
                }while (v.Dot(A[i]).IsTiny());

                __v3rt__ axis = v.Cross(A[i]).Normalized;

                return(__m44rt__.Rotation(axis, angles[i]).TransformDir(A[i]));
            });
        }
 private static __rtype__ RndAngle(RandomSystem rnd)
 => rnd.Uniform__Rtype__() * __cast__Constant.Pi;