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 Elisabeth takes a plane, then it is sunny. If it is sunny, then Elisabeth is taking a plane. If Elisabeth takes a plane, then it is sunny.
Elisabeth is taking a plane if and only if it is sunny can be inferred via the biconditional introduction rule. It is sunny if and only if Elisabeth is taking a plane can be inferred via the biconditional introduction rule. It is sunny if and only if Elisabeth is taking a plane can be inferred via the biconditional introduction rule. Elisabeth is taking a plane if and only if it is sunny can be inferred via the biconditional introduction rule.