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_13, x_13 is not curious. There is at least one x_13 for which x_13 will climb a mountain if and only if x_13 will play squash. For all x_13, x_13 is happy if and only if x_13 will climb a mountain. For all x_13, if x_13 were happy, then x_13 is curious.
For all x_13, x_13 is not happy can be inferred via the universal modus tollens rule. For all x_13, if x_13 were happy, then x_13 is climbing a mountain can be inferred via the universal biconditional elimination rule. There is at least one x_13 for which if x_13 climbs a mountain, then x_13 is playing squash can be inferred via the existential biconditional elimination rule. For all x_13, if x_13 climbs a mountain, then x_13 is happy can be inferred via the universal biconditional elimination rule. There is at least one x_13 for which if x_13 plays squash, then x_13 is climbing a mountain can be inferred via the existential biconditional elimination rule.