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_7, x_7 will drive a car if and only if x_7 is a musician. For all x_14, x_14 is rich if and only if x_14 will write a letter. Susan is not rich. If Richard drives a car, then Susan is writing a letter.
For all x_7, if x_7 drives a car, then x_7 is a musician can be inferred via the universal biconditional elimination rule. For all x_14, if x_14 were rich, then x_14 is writing a letter can be inferred via the universal biconditional elimination rule. For all x_7, if x_7 were a musician, then x_7 is driving a car can be inferred via the universal biconditional elimination rule. For all x_14, if x_14 writes a letter, then x_14 is rich can be inferred via the universal biconditional elimination rule.