Lately I've decided to try and use XeTeX instead of LaTeX when writing documents in LyX in Hebrew, as it was suggested to be more friendly towards different languages. More specifically, I can now use any font I want for both English and Hebrew and Hyperref works like a charm. Installing LyX for use with Hebrew is only slightly more convoluted.
However, I now face one crucial problem - some environments just don't seem to work, and whenever they are added the PDF can't render, with a familiar Undefined control sequence error. Even more strangely, LyX claims the error also concerns other environments which work fine otherwise, such as Part or Section and the like.
The problematic environments seem to be Theorem, Lemma, Corollary, Claim, Definition, Remarks and Proof. Errors only appear when any of these environments are used (Interestingly enough, I can't seem to find a Separator environment, but that is an entirely different matter).
Does anyone know of a solution so I can continue using these environments as I have done previously on LaTeX?