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: Karen is not writing a letter if and only if Barbara is an electrician. It is overcast. If Karen writes a letter, then it is not overcast.
Karen is not writing a letter can be inferred via the modus tollens rule. If Karen doesn't write a letter, then Barbara is an electrician can be inferred via the biconditional elimination rule. If Barbara were an electrician, then Karen is not writing a letter can be inferred via the biconditional elimination rule.