Non-deterministic Schema MathML2

Hello there,

We are trying to parse the PUBMed Central Schema with LXML library.
Unfortunately, the LXML library is fetching an non-deterministic error in
mathml2.

We can't update to mathml3 once we are using a third part schema from PMC.

Wy are we having this error with lxml library, and how can we fix it?

Regards,
*Fabio Batalha C. Santos*
Colegiado SciELO
www.scielo.org
FAPESP - CNPq - BIREME - FapUNIFESP