Question

prove a --> ( b V c ) using contradiction method and combination of inference rules and equivalence laws from these premises : 1. a --> ( d V b ) 2. d --> c

Answer 1

$1. ~~a \to (d \vee b)\\ 2.~~d \to c\\ 3.~~ a \to d~~~~~~~1(addition)\\ 4. ~~a \to c ~~~~~~~(3,1) hpothtical \ syllogism\\$

This is a tautology