Consider the following premises. Thomas is a sailor if and only if Robert is working. Robert is working or Thomas is not a sailor. Can we infer the following from them? If Thomas were a sailor, then Robert is working.
 From the fact that Thomas is a sailor if and only if Robert is working we can infer that if Robert works, then Thomas is a sailor. Finally, from the fact that Robert is working or Thomas is not a sailor we can infer that if Thomas were a sailor, then Robert is working. Therefore, the answer is yes.