What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? Thomas is a writer if and only if it is cold. If Thomas were a writer, then Thomas is writing a letter. If Thomas writes a letter, then Thomas is a writer. Thomas is not writing a letter.
Thomas is not a writer. Thomas is a writer if and only if Thomas is writing a letter. Thomas is writing a letter if and only if Thomas is a writer. If Thomas were a writer, then it is cold. If it is cold, then Thomas is a writer.