Translate the following inference to logic notation: For all x, x_16 will write a letter if and only if x_16 will climb a mountain. For all x, x is not a sailor. Barbara is a taxi driver. Charles is writing a letter if and only if Robert is a sailor. Therefore Charles is not climbing a mountain and Barbara is a taxi driver.
forall x: P(x) <-> Q(x). forall x: ~R(x). p. P(a) <-> R(b). Therefore ~Q(a) and p.