I'm trying to show that this current sentence is tautologic:
[(p∨q)∧(p⇒r)∧(q⇒r)]⇒r
Now I did some calculations and reached this
(¬p∧¬q)∨(p∧¬r)∨(q∧¬r)∨r
Now I'm trying to use Absorption bad unfortunately it does not apply for when you are dealing with a Negation. How should I approach this (final solution is not necessary, more interested in knowing the tools I should use and/or what am I missing)