the category of right comodule of coalgebra is a monoidal category according the following

the associativity constraint is defined as a_{U,V,W}((u\otimes v)\otimes w)=u_0\otimes (v_0\otimes w_0)\Phi(u_1\otimes v_1\otimes w_1), where the coation is \delta(v)=\sum v_0\otimes v_1.

How can we check the Pentagon axiom according the above definition?