Translate the following inference to logic notation: For all x, x_16 is a mechanic if and only if x_16 will cook. For all x, x_16 will cook if and only if x_16 is an electrician. For all x, x_16 is a mechanic or x_16 will write a letter. There is at least one x for which x_16 is not an electrician. Therefore there is at least one x for which x_16 will write a letter.
forall x: P(x) <-> Q(x). forall x: Q(x) <-> R(x). forall x: P(x) or S(x). exists x: ~R(x). Therefore exists x: S(x).