quantities are often denoted by different symbols and terminology. The actual constants are referred to as low-energy constants, parameters or coupling constants in the Lagrangians and sometimes even referred to as counterterms. For the purpose of this review, these are all equivalent.

Another source of confusion is the nomenclature used for the orders. The use in this review is that the contribution to tree-level diagrams from $O(p^2)$ Lagrangians only is called lowest order or order $p^2$ or tree-level. The next order, which consists of tree-level diagrams with one vertex of the $O(p^4)$ Lagrangian and the remaining vertices from the $O(p^2)$ Lagrangian and of one-loop diagrams with only $O(p^2)$ vertices, is called order $p^4$ or next-to-leading order or one-loop order. In the same vein, the third order is called next-to-next-to-leading order or $p^6$ or two-loop order.

When adding other Lagrangians, one needs in addition to specify to which order one has included electromagnetic or weak coupling constants and, if applicable, $m_d-m_u$.

TWO FLAVOURS {#sec:nf2}
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Continuum input {#sec:input2}
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If one looks at the [$n_f=2$]{} Lagrangians we have two parameters at LO, $F$ and $B$, $7+3$ at NLO and $52+4$ at NNLO. The $i+j$ notation refers to the number of LECs 