What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Name the inference rule being used: For all x_7, x_7 is sad if and only if x_7 is a lawyer. It is snowing. If Sarah were a lawyer, then it is not snowing.
Sarah is not a lawyer can be inferred via the modus tollens rule. For all x_7, if x_7 were sad, then x_7 is a lawyer can be inferred via the universal biconditional elimination rule. For all x_7, if x_7 were a lawyer, then x_7 is sad can be inferred via the universal biconditional elimination rule.