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: It is not overcast. It is overcast if and only if Karen is working. Karen is poor.
It is not overcast and Karen is poor can be inferred via the conjunction rule. Karen is poor and it is not overcast can be inferred via the conjunction rule. If it is overcast, then Karen is working can be inferred via the biconditional elimination rule. If Karen works, then it is overcast can be inferred via the biconditional elimination rule. Karen is not working can be inferred via the biconditional elimination rule.