let p, q, r be boolean object ; :: thesis: p => (q <=> r) = ((('not' p) 'or' ('not' q)) 'or' r) '&' ((('not' p) 'or' q) 'or' ('not' r))
( p = FALSE or p = TRUE ) by Def3;
hence p => (q <=> r) = ((('not' p) 'or' ('not' q)) 'or' r) '&' ((('not' p) 'or' q) 'or' ('not' r)) ; :: thesis: verum