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: If Mary plays tennis, then it is late. If it is late, then it is snowing. If it is late, then Mary is playing tennis.
If Mary plays tennis, then it is snowing can be inferred via the transitivity rule. Mary is playing tennis if and only if it is late can be inferred via the biconditional introduction rule. It is late if and only if Mary is playing tennis can be inferred via the biconditional introduction rule.