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 snowing. William is playing squash if and only if Mary is reading a book. If William plays squash, then it is snowing.
William is not playing squash can be inferred via the modus tollens rule. If William plays squash, then Mary is reading a book can be inferred via the biconditional elimination rule. If Mary reads a book, then William is playing squash can be inferred via the biconditional elimination rule.