So here is my problem, I am asked to prove that P $\leftrightarrow$ (Q $\leftrightarrow$ R) is equal to (P $\leftrightarrow$ Q) $\leftrightarrow$ R, pretty straight forward. So I made this truth table to prove it, and the truth values match up perfectly so this proves that they are true. Here is the truth table.
I know the truth table is accurate , but how can I turn this into a proof? They usually start with assume P is true etc.. but I legitmately need an example of transforming this table into that.