The Oberwolfach format is a well-known, specific style of mathematical research workshop originating at the Mathematisches Forschungsinstitut Oberwolfach, and as such represents common knowledge that does not require citation.
The claim describes a well-established institutional fact about mathematical conferencing style (the Oberwolfach workshop format, featuring long periods of unstructured discussion and intensive collaboration in an isolated setting). While the provided papers mention workshops or mention Oberwolfach in passing (such as paper [11] referencing the Oberwolfach Institute), none of them empirically test or are specifically about the definition of the 'Oberwolfach style' itself. The definition of such a conference format is common knowledge in the academic community, making formal citation unnecessary under Step 0.