The question is related to this paper: https://arxiv.org/pdf/1511.06067.pdf
Unfortunately, the meaning of E1(T1,T2), E2(T3), with Tx meaning a tensor, are not specified. It can be found in the proof on the 11th page, which belongs to the theorem on the 4th page.
Could somebody help me what kind of function is Ex(...)? Thank you!