Translate the following inference to logic notation: Jessica is reading a book. For all x, if y were a cashier, then y is sad. If John were sad, then Jessica is not reading a book. If John were sad, then John is a cashier. Therefore John is not a cashier.
p. forall x: P(x) -> Q(x). Q(a) -> ~p. Q(a) -> P(a). Therefore ~P(a).