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_4, z_4 is not an artist. For all z_4, if z_4 were sad, then z_4 is an artist. For all z_4, if z_4 were a scientist, then z_4 is sad. There is at least one z_4 for which if z_4 were an artist, then z_4 is a scientist.
For all z_4, z_4 is not sad can be inferred via the universal modus tollens rule. For all z_4, if z_4 were a scientist, then z_4 is an artist can be inferred via the universal transitivity rule. There is at least one z_4 for which if z_4 were an artist, then z_4 is sad can be inferred via the existential transitivity rule. There is at least one z_4 for which if z_4 were sad, then z_4 is a scientist can be inferred via the existential transitivity rule.