Is $(p \to q) \to r$ logically equivalent to $p \to (q \to r)$? Is $(p \to q) \to r$ logically equivalent to $p \to (q \to r)$?
I try to simply each one, I got $\lnot ( \lnot p \lor q) \lor r$ and $\lnot p \lor ( \lnot q \lor r)$ respectively, 
then I am stuck. Does that mean they aren't equivalent? 
How do I know if expression cannot be further simply? Any tips to solve such questions?
I really appreciate your advise!

No, compare $(p\implies p)\implies r$, which is equivalent to $r$, and $p\implies (p\implies r)$, which is equivalent to $p\implies r$.
