Multi-scale entanglement renormalization ansatz (MERA) includes two kinds of isometric tensors, disentanglers and isometries. Thus tensors in MERA are by definition composed of isometries. Meanwhile we have another tensor network called PEPS. Reading this post (https://physics.stackexchange.com/a/188302/141894), it seems MERA can be represented as PEPS. When constructing MERA from PEPS by reducing tensors, how can one make tensors of PEPS isometric even though PEPS, which includes loops, does not have any canonical form?