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_11, if x_11 were fast, then x_11 is a doctor. There is at least one x_11 for which if x_11 were a doctor, then x_11 is fast. For all x_11, x_11 is fast or x_11 is not a doctor.
For all x_11, if x_11 were a doctor, then x_11 is fast can be inferred via the universal rewriting rule. There is at least one x_11 for which x_11 is a doctor if and only if x_11 is fast can be inferred via the existential biconditional introduction rule. There is at least one x_11 for which x_11 is fast if and only if x_11 is a doctor can be inferred via the existential biconditional introduction rule.