Fitch Proof Exercise 13.8

Question

I am having trouble solving this Fitch Proof. Here is how far I’ve gotten

Only the last step is not checked out in Fitch but I think the logic works well.

Any help is appreciated.

Thank you

Answer 1

$$\begin{array} {rl} & \forall x .(Cx \to \forall y. (Dy \to Fxy)) \\ & \quad \boxed{b} \\ & \quad \quad \boxed{c} \\ & \quad \quad \quad Cb \land Dc \\ & \quad \quad \quad \vdots \\ & \quad \quad \quad Fbc \\ & \quad \quad (Cb \land Dc) \to Fbc \\ & \quad \forall y .(Cb \land Dy) \to Fby \\ & \forall x .\forall y. (Cx \land Dy) \to Fxy \\ \end{array}$$

Organizing your proof like this may work. Unfortunately the software is closed so it can't be openly verified.