Consider the following premises. Mary is a mechanic if and only if it is sunny. Charles is a server if and only if Mary is a mechanic. It is not sunny. Charles is a server if and only if Robert is happy. Can we infer the following from them? Robert is happy.
 From the fact that Mary is a mechanic if and only if it is sunny, and that it is not sunny we can infer that Mary is not a mechanic. From the fact that Charles is a server if and only if Mary is a mechanic, and that Mary is not a mechanic we can infer that Charles is not a server. Finally, from the fact that Charles is a server if and only if Robert is happy, and that Charles is not a server we can infer that Robert is not happy, which contradicts that Robert is happy. Therefore, the answer is no.