On the Diophantine system $$f(z)\,{=}\,f(x)f(y)\,{=}\,f(u) f(v)$$f(z)=f(x)f(y)=f(u)f(v)

We show that the Diophantine system $$\begin{aligned} f(z)=f(x)f(y)=f(u)f(v) \end{aligned}$$f(z)=f(x)f(y)=f(u)f(v)has infinitely many nontrivial positive integer solutions for $$f(X)=X^2-1$$f(X)=X2-1, and infinitely many nontrivial rational solutions for $$f(X)=X^2+b$$f(X)=X2+b with nonzero integer b.