  In this work we present a strong chiral meson Lagrangian up to and including
$O(p^6)$ in the momentum expansion. It is derived from the Nambu--Jona-Lasinio
(NJL) model using the heat-kernel method. Identities related to the properties
of covariant derivatives of the chiral matrix $U$ as well as field
transformations have been used to obtain a minimal set of linearly independent
terms.
