Complex sentence: Such stacks of branes are inconsistent in a non-torsion NS 3-form background, which, as was highlighted by Anton Kapustin in hep-th/9909089, complicates the extension of the K-theory classification to such cases.
Split into simpler sentences: Such stacks of branes are inconsistent in a non-torsion NS 3-form background, which, as was highlighted by Anton Kapustin in hep-th/9909089. This complicates the extension of the K-theory classification to such cases.