What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If Richard makes tea, then John is taking a plane. John is not taking a plane. If Richard makes tea, then Robert is a lawyer. If Robert were a lawyer, then Richard is making tea.
Richard is not making tea. If Robert were a lawyer, then John is taking a plane. Richard is making tea if and only if Robert is a lawyer. Robert is a lawyer if and only if Richard is making tea.