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, x_11 will climb a mountain if and only if x_11 will play squash. For all x_11, if x_11 goes running, then x_11 is climbing a mountain. For all x_11, x_11 is sad if and only if x_11 will go running.
For all x_11, if x_11 climbs a mountain, then x_11 is playing squash can be inferred via the universal biconditional elimination rule. For all x_11, if x_11 were sad, then x_11 is running can be inferred via the universal biconditional elimination rule. For all x_11, if x_11 plays squash, then x_11 is climbing a mountain can be inferred via the universal biconditional elimination rule. For all x_11, if x_11 goes running, then x_11 is sad can be inferred via the universal biconditional elimination rule.