Figure 1: (a) A schematic Fermi surface extracted from quantum oscillation measurements by Sebastian et al. The authors argue that they can extract from the data both electron and hole pockets ($\alpha$ and $\beta$ are hole pockets, and $\gamma$ are electron pockets). (b) Reconstructed Fermi surface for incommensurate SDW order in low-disorder ortho-II phase of ${\text{YBCO}}_{6+\delta }$.