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_17, if x_17 were a mechanic, then x_17 is a server. There is at least one x_17 for which x_17 is an office clerk. For all x_17, if x_17 were a server, then x_17 is a mechanic. For all x_17, x_17 is a soldier if and only if x_17 is a mechanic. For all x_17, if x_17 were a soldier, then x_17 is not an office clerk.
There is at least one x_17 for which x_17 is not a soldier can be inferred via the existential modus tollens rule. For all x_17, x_17 is a mechanic if and only if x_17 is a server can be inferred via the universal biconditional introduction rule. For all x_17, x_17 is a server if and only if x_17 is a mechanic can be inferred via the universal biconditional introduction rule. For all x_17, if x_17 were a soldier, then x_17 is a mechanic can be inferred via the universal biconditional elimination rule. For all x_17, if x_17 were a mechanic, then x_17 is a soldier can be inferred via the universal biconditional elimination rule.