ProofWiki:Sandbox

{|class = 'sortable' id='3' !Line!!Pool!!Formula!!Rule!!Depends upon 1 1 $$p$$ $$P$$ }
 * -class='sortbottom'
 * -class='sortbottom'
 * -class='sortbottom'

$$p \lor \left({q \lor r}\right) \vdash \left({p \lor q}\right) \lor r$$: