What can be inferred from the following premises in a single inference step (ignoring inferences that add new predicates or constants)? It is snowing if and only if it is cold. It is sunny if and only if David is taking a plane. David is taking a plane if and only if it is cold. It is not snowing. It is sunny if and only if Joseph is writing a letter.
If it snows, then it is cold. If it is sunny, then David is taking a plane. If David takes a plane, then it is cold. If it is sunny, then Joseph is writing a letter. If it is cold, then it is snowing. If David takes a plane, then it is sunny. If it is cold, then David is taking a plane. If Joseph writes a letter, then it is sunny. It is not cold.