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_6, x_6 is a scientist or x_6 is a server. For all x_6, if x_6 were poor, then x_6 is happy. For all x_6, if x_6 were a server, then x_6 is poor. There is at least one x_6 for which x_6 is happy if and only if x_6 is a scientist.
For all x_6, if x_6 were a server, then x_6 is happy can be inferred via the universal transitivity rule. There is at least one x_6 for which if x_6 were happy, then x_6 is a scientist can be inferred via the existential biconditional elimination rule. There is at least one x_6 for which if x_6 were a scientist, then x_6 is happy can be inferred via the existential biconditional elimination rule.