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 for which x will drink water. For all x, x is poor. For all x, x will write a letter if and only if x will drink water.
There is at least one x for which x will drink water and x is poor can be inferred via the existential conjunction rule. There is at least one x for which x is poor and x will drink water can be inferred via the existential conjunction rule. For all x, if x writes a letter, then x is drinking water can be inferred via the universal biconditional elimination rule. For all x, if x drinks water, then x is writing a letter can be inferred via the universal biconditional elimination rule.