How do I prove this? (propositional logic) 1. The problem statement, all variables and given/known data How to prove this [itex](p \rightarrow (q \vee p)) \rightarrow r \vdash \neg p \vee (q \vee r)[/itex] using only the natural deduction rules in propositional logic? 2. Relevant equations http://en.wikipedia.org/wiki/Propositional_logic (natural deduction rules only) 3. The attempt at a solution [itex]1: (p \rightarrow (q \vee p)) \rightarrow r[/itex] premise <start of hypothesis 0> ; I tried to make a box here but failed miserably [itex]2: \neg (\neg p \vee (q \vee r))[/itex] hypothesis <start of hypothesis 1> [itex]3: \neg p[/itex] hypothesis [itex]4: \neg p \vee (q \vee r)[/itex] conjunction introduction 3 [itex]5: \bot[/itex] negation introduction 2,4 <end of hypothesis 1> [itex]6: \neg \neg p[/itex] negation introduction 3-5 [itex]7: p[/itex] double negative elimination 6 [itex]8: ?[/itex] <end of hypothesis 0> As you can see, I don't exactly know how to use TeX. PS: How do I put a box around the hypothesis in TeX?