What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? If it is sunny, then Mary is sad. If Mary were sad, then Thomas is writing a letter. It is sunny if and only if Thomas is writing a letter.
If it is sunny, then Thomas is writing a letter. If it is sunny, then Thomas is writing a letter. If Thomas writes a letter, then it is sunny.