Consider the following premises. Robert is rich if and only if Linda is taking a plane. David is playing tennis if and only if Linda is taking a plane. If Linda takes a plane, then Robert is rich. David is not playing tennis. Can we infer the following from them? If we can, name the inference rule being used: Robert is rich.
 From the fact that Robert is rich if and only if Linda is taking a plane we can infer that if Robert were rich, then Linda is taking a plane via biconditional elimination. From the fact that if Robert were rich, then Linda is taking a plane, and that if Linda takes a plane, then Robert is rich we can infer that Robert is rich if and only if Linda is taking a plane via biconditional introduction. From the fact that David is playing tennis if and only if Linda is taking a plane, and that David is not playing tennis we can infer that Linda is not taking a plane via biconditional elimination. Finally, from the fact that Robert is rich if and only if Linda is taking a plane, and that Linda is not taking a plane we can infer that Robert is not rich via biconditional elimination, which contradicts that Robert is rich. Therefore, the answer is no.