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, y will not climb a mountain. For all y, y is a taxi driver if and only if y is a lawyer. There is at least one y for which if y climbs a mountain, then y is a taxi driver. For all y, if y were a taxi driver, then y is climbing a mountain.
For all y, y is not a taxi driver can be inferred via the universal modus tollens rule. There is at least one y for which y will climb a mountain if and only if y is a taxi driver can be inferred via the existential biconditional introduction rule. There is at least one y for which y is a taxi driver if and only if y will climb a mountain can be inferred via the existential biconditional introduction rule. For all y, if y were a taxi driver, then y is a lawyer can be inferred via the universal biconditional elimination rule. For all y, if y were a lawyer, then y is a taxi driver can be inferred via the universal biconditional elimination rule.