In case you needed any more evidence that trying to use MathML in place of LaTeX only causes trouble, here's the BibTeX generated by Elsevier for one of their papers (curl -LH "Accept: application/x-bibtex" http://dx.doi.org/10.1016/j.ejc.2011.12.005).

And in case you're wondering what that big glob of junk in the title should have been: it's $\chi$. Or even χ, if you're feeling sloppy. If I'm criticizing Elsevier here, though, I have to also credit them with getting the diacritics in the names correct; many other sources wouldn't have. The doi/url duplication and the unnecessary publisher field are standard for dois obtained through this method and are not Elsevier's fault.

@article{Dvo_k_2012,
doi = {10.1016/j.ejc.2011.12.005},
url = {https://doi.org/10.1016%2Fj.ejc.2011.12.005},
year = 2012,
month = {may},
publisher = {Elsevier {BV}},
volume = {33},
number = {4},
pages = {679--683},
author = {Zden{\v{e}}k Dvo{\v{r}}{\'{a}}k and Daniel Kr{\'{a}}l'},
title = {Classes of graphs with small rank decompositions are $\less$mml:math altimg="si1.gif" display="inline" overflow="scroll" xmlns:xocs="http://www.elsevier.com/xml/xocs/dtd" xmlns:xs="http://www.w3.org/2001/{XMLSchema}" xmlns:xsi="http://www.w3.org/2001/{XMLSchema}-instance" xmlns="http://www.elsevier.com/xml/ja/dtd" xmlns:ja="http://www.elsevier.com/xml/ja/dtd" xmlns:mml="http://www.w3.org/1998/Math/{MathML}" xmlns:tb="http://www.elsevier.com/xml/common/table/dtd" xmlns:sb="http://www.elsevier.com/xml/common/struct-bib/dtd" xmlns:ce="http://www.elsevier.com/xml/common/dtd" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:cals="http://www.elsevier.com/xml/common/cals/dtd"$\greater$$\lessmml:mi\greater$$\upchi$$\less/mml:mi\greater$$\less$/mml:math$\greater$-bounded},
journal = {European Journal of Combinatorics}
}