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: Sarah is writing a letter if and only if it is cold. It is raining or Sarah is writing a letter. It is not raining or David is a sailor. It is not cold.
Sarah is writing a letter or David is a sailor can be inferred via the resolution rule. If Sarah writes a letter, then it is cold can be inferred via the biconditional elimination rule. If it is cold, then Sarah is writing a letter can be inferred via the biconditional elimination rule. Sarah is not writing a letter can be inferred via the biconditional elimination rule.