R equals quaternion rotation: True n = 10398
R^T R = I: True  det R = 1: True
a1: on ray from y and on rotated ray from x': True
a2: on ray from y and on rotated ray from x': True
a3: on ray from y and on rotated ray from x': True
a1, a2 as stated: True
a3 = lam*(-22/25,-27/100,-22/25): True  lam ~ 1.1277699452865664
CONSTRUCTION CHECK: OK
