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, if z were happy, then z is an artist. For all z, if z were an artist, then z is happy. For all z, z is not happy.
For all z, z is not an artist can be inferred via the universal modus tollens rule. For all z, z is happy if and only if z is an artist can be inferred via the universal biconditional introduction rule. For all z, z is an artist if and only if z is happy can be inferred via the universal biconditional introduction rule.