more contributors, RBC/UKQCD [@Arthur:2012opa], MILC [@Bazavov:2010yq], NPLQCD [@Beane:2011zm] and BMW [@Borsanyi:2012zv]. For a more complete reference list, including $N_f=2$, see Ref. [@Aoki:2013ldr]. The FLAG results for $N_f=2$ and $N_f=2+1+1$ are dominated by the ETM results [@Baron:2009wt] and [@Baron:2011sf], respectively, while the $N_f=2+1$ results are averaged over several collaborations, which are not always in good agreement. This is the reason why the errors for the $N_f=2+1$ case as quoted below are larger. The results quoted are always those when the various $N_f$ cases have been analysed with [$n_f=2$]{} [ChPT]{}. FLAG [@Aoki:2013ldr] gives the averages $$\begin{aligned}
\label{eq:flagsu2}
\left.\bar l_3\right|_{N_f=2} &=& 3.45\pm0.26\,,\quad
\left.\bar l_3\right|_{N_f=2+1} = 2.77\pm1.27\,,\quad
\left.\bar l_3\right|_{N_f=2+1+1} = 3.70\pm0.27\,,
\nonumber \\
\left.\bar l_4\right|_{N_f=2} &=& 4.59\pm0.26\,,\left.\bar l_4\right|_{N_f=2+1} = 3.95\pm0.35\,,\quad
\left.\bar l_4\right|_{N_f=2+1+1} = 4.67\pm0.10\,.
\nonumber \\
 & &\end{aligned}$$ Clearly, there is still a significant spread in central values. Not included in the FLAG averages (\[eq:flagsu2\]) are the more recent $N_f=2+1$ results [@Durr:2013goa] $\bar l_3 = 2.5\pm
  0.7$ and $\bar l_4 = 3.8\pm0.5$.

A rough estimate that covers the lattice range and the continuum results (\[eq:l3\],\[eq:l4\]) is $$\label{eq:l3l4}
\bar l_3 = 3.0\pm0.8\,,\quad
\bar l_4 = 4.3\pm0.3\,.$$ These are what we will use in the fits for the [$n_f=3$]{} constants below.

THREE FLAVOURS {#sec:nf3}
==============

New 