How do I ask about an open-book exam when my textbook is digital and devices are banned?

The exam notice says "one printed textbook permitted; no electronic devices." I bought the digital edition in September because it was the less expensive option.

The lecturer used it in class and never mentioned a printed-book requirement. Now the exam is two weeks away. A used copy of the current edition is listed at $85. The library has two copies, but neither is available to reserve for that morning. I found an older edition I could borrow, with different page numbers and some missing case studies.

I don't want to turn up with a tablet and argue at the door. What should I ask the lecturer before spending the money? I'd be happy to use approved printed extracts if those are permitted, but I don't want to assume I can print a whole book or bring materials the other students weren't allowed.