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 x_4, if x_4 were a scientist, then x_4 is a sailor. For all x_4, x_4 is not an office clerk. For all x_4, if x_4 were an office clerk, then x_4 is a scientist. There is at least one x_4 for which if x_4 were a sailor, then x_4 is an office clerk.
There is at least one x_4 for which x_4 is not a sailor can be inferred via the existential modus tollens rule. For all x_4, if x_4 were an office clerk, then x_4 is a sailor can be inferred via the universal transitivity rule. There is at least one x_4 for which if x_4 were a sailor, then x_4 is a scientist can be inferred via the existential transitivity rule. There is at least one x_4 for which if x_4 were a scientist, then x_4 is an office clerk can be inferred via the existential transitivity rule.