Consider the following premises. If Susan were fast, then James is a janitor. If it is sunny, then Susan is fast. If Susan were an office clerk, then it is sunny. If James were a janitor, then Susan is an office clerk. Can we infer the following from them? It is sunny if and only if Susan is an office clerk.
 From the fact that if Susan were fast, then James is a janitor, and that if James were a janitor, then Susan is an office clerk we can infer that if Susan were fast, then Susan is an office clerk. From the fact that if it is sunny, then Susan is fast, and that if Susan were fast, then Susan is an office clerk we can infer that if it is sunny, then Susan is an office clerk. Finally, from the fact that if it is sunny, then Susan is an office clerk, and that if Susan were an office clerk, then it is sunny we can infer that it is sunny if and only if Susan is an office clerk. Therefore, the answer is yes.