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_5, x_5 is not a server. For all x_5, if x_5 works, then x_5 is a server. For all x_5, x_5 will work if and only if x_5 is sad.
For all x_5, x_5 will not work can be inferred via the universal modus tollens rule. For all x_5, if x_5 works, then x_5 is sad can be inferred via the universal biconditional elimination rule. For all x_5, if x_5 were sad, then x_5 is working can be inferred via the universal biconditional elimination rule.