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 playing a game or William is not happy. Sarah is playing a game if and only if Susan is poor.
If William were happy, then Sarah is playing a game can be inferred via the rewriting rule. If Sarah plays a game, then Susan is poor can be inferred via the biconditional elimination rule. If Susan were poor, then Sarah is playing a game can be inferred via the biconditional elimination rule.