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 z for which z will not drink water. For all z, z is happy or z is not a writer. For all z, z will drink water if and only if z is happy.
For all z, if z were a writer, then z is happy can be inferred via the universal rewriting rule. For all z, if z drinks water, then z is happy can be inferred via the universal biconditional elimination rule. For all z, if z were happy, then z is drinking water can be inferred via the universal biconditional elimination rule. There is at least one z for which z is not happy can be inferred via the existential biconditional elimination rule.