What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? For all x_12, x_12 is a doctor. For all x_12, if x_12 writes a letter, then x_12 is not a doctor. Barbara is writing a letter if and only if Richard is making tea.
If Barbara writes a letter, then Richard is making tea. If Richard makes tea, then Barbara is writing a letter. For all x_12, x_12 will not write a letter.