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: If it is overcast, then Charles is working. Charles is working if and only if it is overcast. If Charles works, then it is overcast.
It is overcast if and only if Charles is working can be inferred via the biconditional introduction rule. Charles is working if and only if it is overcast can be inferred via the biconditional introduction rule. If Charles works, then it is overcast can be inferred via the biconditional elimination rule. If it is overcast, then Charles is working can be inferred via the biconditional elimination rule.