The order p 8 mesonic chiral Lagrangian
We derive the chiral Lagrangian at next-to-next-to-next-to-leading order (NNNLO) for a general number Nf of light quark flavours as well as for Nf = 2, 3. We enumerate the contact terms separately. We also discuss the cases where some of the external fields are not included. An example of a choice of Lagrangian is given in the supplementary material.