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!

It is not. Suppose $p$, $q$, $r$ are false. Then $p \rightarrow q$ and $q \rightarrow r$ are true, so $(p\rightarrow q)\rightarrow r$ is false and $p\rightarrow (q\rightarrow r)$ is true.
