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_10, if x_10 writes a letter, then x_10 is running. For all x_10, if x_10 goes running, then x_10 is writing a letter. There is at least one x_10 for which x_10 will drive a car if and only if x_10 will write a letter.
For all x_10, x_10 will write a letter if and only if x_10 will go running can be inferred via the universal biconditional introduction rule. For all x_10, x_10 will go running if and only if x_10 will write a letter can be inferred via the universal biconditional introduction rule. There is at least one x_10 for which if x_10 drives a car, then x_10 is writing a letter can be inferred via the existential biconditional elimination rule. There is at least one x_10 for which if x_10 writes a letter, then x_10 is driving a car can be inferred via the existential biconditional elimination rule.