Electrical and Control Engineering: Transfer Function Reduction problem

I am having a problem with calculating transfer function given with a picture below i need to calculate output Y(p) / input V(p) analitically. Here are the equasions, i dont know the equasion for a and z Y= fN = (F(p+r))N = F(P(z+m+f)+ROv) p=P(z+m+f)
r = Ro=ROv
b = Bo=BOv
o = Ov
f = F(p+r)
m = M(b-a)
a = A ???
z = Z ???


Thanks for any help or comment