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_18, x_18 is a lawyer if and only if x_18 is a taxi driver. It is not cloudy. Robert is a taxi driver if and only if it is cloudy. Sarah is a mechanic.
It is not cloudy and Sarah is a mechanic can be inferred via the conjunction rule. Sarah is a mechanic and it is not cloudy can be inferred via the conjunction rule. If Robert were a taxi driver, then it is cloudy can be inferred via the biconditional elimination rule. If it is cloudy, then Robert is a taxi driver can be inferred via the biconditional elimination rule. Robert is not a taxi driver can be inferred via the biconditional elimination rule. For all x_18, if x_18 were a lawyer, then x_18 is a taxi driver can be inferred via the universal biconditional elimination rule. For all x_18, if x_18 were a taxi driver, then x_18 is a lawyer can be inferred via the universal biconditional elimination rule.