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_8 for which x_8 is not happy. For all x_8, if x_8 were a lawyer, then x_8 is climbing a mountain. For all x_8, x_8 will climb a mountain if and only if x_8 is happy.
For all x_8, if x_8 climbs a mountain, then x_8 is happy can be inferred via the universal biconditional elimination rule. For all x_8, if x_8 were happy, then x_8 is climbing a mountain can be inferred via the universal biconditional elimination rule. There is at least one x_8 for which x_8 will not climb a mountain can be inferred via the existential biconditional elimination rule.