Consider the following premises. Susan is a cashier and Elisabeth is writing a letter. If David were fast, then Susan is not a cashier. Barbara is a scientist. Can we infer the following from them? If we can, name the inference rule being used: David is fast.
 From the fact that Susan is a cashier and Elisabeth is writing a letter we can infer that Susan is a cashier via simplification. Finally, from the fact that if David were fast, then Susan is not a cashier, and that Susan is a cashier we can infer that David is not fast via modus tollens, which contradicts that David is fast. Therefore, the answer is no.