  We derive the chiral Lagrangian at next-to-next-to-next-to-leading order
(NNNLO) for a general number $N_f$ of light quark flavours as well as for
$N_f=2,3$. 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.
