Concerning this subject, I consulted the following Wikipedia page: Universal joint
where the elementary kinematics equation of the U-joint is stated.
But, a little bit further in the article Double Cardan Shaft
where the configuration described consists of 2 U-joints, the previously mentioned equation is reversed, i.e:
$\tan \gamma _{1}=\cos \beta \tan \gamma _{2}$,
$\tan \gamma _{2}=\cos \beta \,\tan \gamma _{1}\qquad \tan \gamma _{4}=\cos \beta \,\tan \gamma _{3}$
I do not intend to doubt the validity of the info on the article, but this hit me as a pretty weird thing.
Are these relationships correct?