Integrating out strange quarks in ChPT

We study three flavour chiral perturbation theory in a limit where the strange quark mass is much larger than the external momenta and the up and down quark masses, and where the external fields are those of two–flavour chiral perturbation theory. In this case, the theory reduces to the one of SU(2)L × SU(2)R. Through this reduction, one can work out the strange quark mass dependence of the LECs in the two–flavour case. We present the pertinent relations at two–loop order for F,B and li.