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 Charles writes a letter, then it is snowing. It is not cloudy. Charles is writing a letter if and only if it is snowing. It is cloudy if and only if it is snowing.
If Charles writes a letter, then it is snowing can be inferred via the biconditional elimination rule. If it is cloudy, then it is snowing can be inferred via the biconditional elimination rule. If it snows, then Charles is writing a letter can be inferred via the biconditional elimination rule. If it snows, then it is cloudy can be inferred via the biconditional elimination rule. It is not snowing can be inferred via the biconditional elimination rule.