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 plays tennis, then it is sunny. William is not playing tennis. If William plays tennis, then it is sunny. If it is sunny, then William is playing tennis.
It is not sunny can be inferred via the modus tollens rule. William is playing tennis if and only if it is sunny can be inferred via the biconditional introduction rule. William is playing tennis if and only if it is sunny can be inferred via the biconditional introduction rule. It is sunny if and only if William is playing tennis can be inferred via the biconditional introduction rule. It is sunny if and only if William is playing tennis can be inferred via the biconditional introduction rule.