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 cloudy. Mary is playing tennis if and only if Patricia is writing a letter. Patricia is writing a letter or it is not cloudy. If Patricia writes a letter, then it is cloudy.
Patricia is not writing a letter can be inferred via the modus tollens rule. If it is cloudy, then Patricia is writing a letter can be inferred via the rewriting rule. If Mary plays tennis, then Patricia is writing a letter can be inferred via the biconditional elimination rule. If Patricia writes a letter, then Mary is playing tennis can be inferred via the biconditional elimination rule.