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_7, x_7 will drink water if and only if x_7 is a doctor. There is at least one x_7 for which if x_7 climbs a mountain, then x_7 is sad. For all x_7, if x_7 were sad, then x_7 is drinking water.
There is at least one x_7 for which if x_7 climbs a mountain, then x_7 is drinking water can be inferred via the existential transitivity rule. For all x_7, if x_7 drinks water, then x_7 is a doctor can be inferred via the universal biconditional elimination rule. For all x_7, if x_7 were a doctor, then x_7 is drinking water can be inferred via the universal biconditional elimination rule.