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: David is a carpenter if and only if it is cold. For all z_2, z_2 is not a carpenter.
If David were a carpenter, then it is cold can be inferred via the biconditional elimination rule. If it is cold, then David is a carpenter can be inferred via the biconditional elimination rule.