Consider the following premises. It is not windy. It is snowing. If Thomas writes a letter, then Mary is a carpenter. It is windy if and only if Mary is a carpenter. Can we infer the following from them? If we can, name the inference rule being used: Thomas is writing a letter.
 From the fact that it is windy if and only if Mary is a carpenter, and that it is not windy we can infer that Mary is not a carpenter via biconditional elimination. Finally, from the fact that if Thomas writes a letter, then Mary is a carpenter, and that Mary is not a carpenter we can infer that Thomas is not writing a letter via modus tollens, which contradicts that Thomas is writing a letter. Therefore, the answer is no.