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 z, z will not make tea. There is at least one z for which if z were sad, then z is making tea. For all z, if z makes tea, then z is sad. For all z, if z makes tea, then z is sad.
There is at least one z for which z is not sad can be inferred via the existential modus tollens rule. There is at least one z for which z is sad if and only if z will make tea can be inferred via the existential biconditional introduction rule. There is at least one z for which z is sad if and only if z will make tea can be inferred via the existential biconditional introduction rule. There is at least one z for which z will make tea if and only if z is sad can be inferred via the existential biconditional introduction rule. There is at least one z for which z will make tea if and only if z is sad can be inferred via the existential biconditional introduction rule.