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: Richard is playing squash if and only if Charles is reading a book. If Susan works, then Richard is playing squash. Joseph is playing tennis or Charles is not reading a book. Joseph is not playing tennis.
Charles is not reading a book can be inferred via the disjunctive syllogism rule. If Charles reads a book, then Joseph is playing tennis can be inferred via the rewriting rule. If Richard plays squash, then Charles is reading a book can be inferred via the biconditional elimination rule. If Charles reads a book, then Richard is playing squash can be inferred via the biconditional elimination rule.