Clarification on some equalities in the frame kinematics white paper

[Ashesh Sharma]

Hello,

I have been trying to read up on quaternion algebra, and came across the white papers documentation for Chrono. This is a very helpful resource. I have been able to follow the rotations document, however have run into issues with the frame kinematics document. 

Specifically, I am struggling to understand, on page 5 in the section Product: the velocity part, how does the following hold true - 

dq(b,c)/dt . r(a,b) . q*(b,c) + q(b,c) . r(a,b) . dq*(b,c)/dt = 2 dq(b,c)/dt . r(a,b) . q*(b,c)

Best,
Ashesh Sharma