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_1, if x_1 makes tea, then x_1 is climbing a mountain. For all x_1, if x_1 climbs a mountain, then x_1 is making tea.
For all x_1, x_1 will make tea if and only if x_1 will climb a mountain can be inferred via the universal biconditional introduction rule. For all x_1, x_1 will climb a mountain if and only if x_1 will make tea can be inferred via the universal biconditional introduction rule.