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 y, if y were poor, then y is a taxi driver. For all y, if y were a taxi driver, then y is poor. For all y, if y were a taxi driver, then y is poor.
For all y, y is poor if and only if y is a taxi driver can be inferred via the universal biconditional introduction rule. For all y, y is poor if and only if y is a taxi driver can be inferred via the universal biconditional introduction rule. For all y, y is a taxi driver if and only if y is poor can be inferred via the universal biconditional introduction rule. For all y, y is a taxi driver if and only if y is poor can be inferred via the universal biconditional introduction rule.