Translate the following inference to logic notation: For all x, x_7 is a cashier or x_7 will make tea. For all x, x_7 is a cashier if and only if x_7 is a musician. There is at least one x for which x_7 is a musician or x_7 will not make tea. Therefore there is at least one x for which x_7 is a musician.
forall x: P(x) or Q(x). forall x: P(x) <-> R(x). exists x: R(x) or ~Q(x). Therefore exists x: R(x).