Consider the following premises. If Michael plays squash, then Jennifer is writing a letter. Barbara is a police officer if and only if Jennifer is writing a letter. If Jennifer writes a letter, then Robert is running. Barbara is a police officer or Michael is playing squash. Can we infer the following from them? Robert is not running.
 From the fact that Barbara is a police officer if and only if Jennifer is writing a letter we can infer that if Barbara were a police officer, then Jennifer is writing a letter. From the fact that if Barbara were a police officer, then Jennifer is writing a letter, that if Michael plays squash, then Jennifer is writing a letter, and that Barbara is a police officer or Michael is playing squash we can infer that Jennifer is writing a letter. Finally, from the fact that if Jennifer writes a letter, then Robert is running, and that Jennifer is writing a letter we can infer that Robert is running, which contradicts that Robert is not running. Therefore, the answer is no.