7) (12 points) Consider the following argument and express the argument bellow, using propositional variables f, b and l. Is this argument valid? If so, prove its validity or if not, state why it is not valid. Fry and Bender are not both innocent. If Fry is not lying, Bender must be innocent. Therefore, if Fry is innocent, then he is lying Let f be the proposition "Fry is innocent" Let b be the proposition "Bender is innocent" Let l be the proposition "Fry is lying". int: Statement VxVy P(x, y) YyVxP(x, y) When True? P(x,y) is true for every pair x, y. When False? There is a pair x, y for which P(x, y) is false There is an r such that there is a yfor