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: It is sunny or it is windy. If Sarah were rich, then it is not windy. Sarah is not writing a letter. It is sunny if and only if Sarah is writing a letter.
If it is sunny, then Sarah is writing a letter can be inferred via the biconditional elimination rule. If Sarah writes a letter, then it is sunny can be inferred via the biconditional elimination rule. It is not sunny can be inferred via the biconditional elimination rule.