If L turns head-to-wind (but not beyond) in such a manner that W cannot keep clear by also turning head-to-wind (but not beyond) in a seamanlike way, then L breaks rule 16.1.

Provided she complies with RRS 18.2(b), RRS 17 (if applicable) and RRS 16.1, L may turn head-to-wind. W must respond and keep clear per RRS 11 (or 12, whichever is applicable), but W is not under any obligation to tack, and L cannot compel her to.

I think we've beaten this topic to death, and I'm certainly tired of repeating myself so please, if you still think that a boat is required to tack at a mark, quote the rule that says so.

Regards,
Eric