Translate the following inference to logic notation: For all x, y_1 will make tea if and only if y_1 will write a letter. David is writing a letter if and only if Robert is a scientist. For all x, x_12 is not a scientist. Therefore David is not making tea.
forall x: P(x) <-> Q(x). Q(a) <-> R(b). forall x: ~R(x). Therefore ~P(a).