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: There is at least one x_7 for which x_7 is a musician if and only if x_7 is a politician. For all x_7, x_7 is a musician or x_7 is not a politician.
For all x_7, if x_7 were a politician, then x_7 is a musician can be inferred via the universal rewriting rule. There is at least one x_7 for which if x_7 were a musician, then x_7 is a politician can be inferred via the existential biconditional elimination rule. There is at least one x_7 for which if x_7 were a politician, then x_7 is a musician can be inferred via the existential biconditional elimination rule.