I am reading this book "a guide to quantum groups" written by V.C. and A.P. But the proof of propersition 4.2.3 on page 121 confused me.
Just this place " Applying $id \bigotimes S \bigotimes S^2$ to both sides and reversing the order of the factors ,we obtain ...." My question is why the equation we obtain doesn't have the symbol $\bigotimes$? Why LHS equals to RHS after multiplication?