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: William is excited if and only if Sarah is a taxi driver. Susan is not a doctor or it is cloudy. Susan is a doctor or Sarah is a taxi driver. William is not excited.
Sarah is a taxi driver or it is cloudy can be inferred via the resolution rule. If William were excited, then Sarah is a taxi driver can be inferred via the biconditional elimination rule. If Sarah were a taxi driver, then William is excited can be inferred via the biconditional elimination rule. Sarah is not a taxi driver can be inferred via the biconditional elimination rule.