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_12, x_12 is a musician if and only if x_12 is happy. For all x_12, if x_12 were happy, then x_12 is a doctor. Richard is not a doctor.
For all x_12, if x_12 were a musician, then x_12 is happy can be inferred via the universal biconditional elimination rule. For all x_12, if x_12 were happy, then x_12 is a musician can be inferred via the universal biconditional elimination rule.