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