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: If William were happy, then it is snowing. If David cooks, then it is snowing. David is cooking or it is sunny. It is raining if and only if it is snowing. If it is sunny, then William is happy.
If it is sunny, then it is snowing can be inferred via the transitivity rule. If it rains, then it is snowing can be inferred via the biconditional elimination rule. If it snows, then it is raining can be inferred via the biconditional elimination rule.