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 late if and only if Richard is writing a letter. Karen is poor. Richard is not writing a letter. Richard is writing a letter or it is not late.
It is not late can be inferred via the disjunctive syllogism rule. Karen is poor and Richard is not writing a letter can be inferred via the conjunction rule. Richard is not writing a letter and Karen is poor can be inferred via the conjunction rule. If it is late, then Richard is writing a letter can be inferred via the rewriting rule. If it is late, then Richard is writing a letter can be inferred via the biconditional elimination rule. If Richard writes a letter, then it is late can be inferred via the biconditional elimination rule. It is not late can be inferred via the biconditional elimination rule.