Consider the following premises. If David plays squash, then Thomas is a police officer. If Thomas were a police officer, then John is a mechanic. David is playing squash if and only if John is a mechanic. Can we infer the following from them? The fact that John were a mechanic does not imply that David is playing squash.
 From the fact that if David plays squash, then Thomas is a police officer, and that if Thomas were a police officer, then John is a mechanic we can infer that if David plays squash, then John is a mechanic. Finally, from the fact that David is playing squash if and only if John is a mechanic we can infer that if John were a mechanic, then David is playing squash, which contradicts that The fact that John were a mechanic does not imply that David is playing squash. Therefore, the answer is no.